At only 20, FC Barcelona's current idol Lionel Messi is, according to Ronaldinho, the best footballer in the world. Slightly built and extravagantly gifted, the Argentinian is the heir apparent to Diego Maradona but, Messi says, he is not interested in imitating anyone

Fabio Capello called him il diavolo, Italian for 'the devil'. In Argentina he is la pulga, Spanish for 'the flea'. His Cameroonian team-mate Samuel Eto'o says that seeing him play is like watching dibujos animados, Spanish for 'animated pictures', best translated as 'cartoons'.

All of them are right. There is something tail-swishingly devilish about the way Lionel Messi runs with a football; he is as hard to catch as a flea; the speed with which he nips past rival defenders is eye-deceivingly, cartoonishly improbable. No doubt about it: the 20-year-old, 5ft 7in Argentinian is poised - along with Cristiano Ronaldo and Cesc Fábregas - to take over from Zidane, Ronaldo and Messi's Barcelona team-mate Ronaldinho as one of the great players of the next decade. The young trio will be adorning the rest of this season's Champions League, which resumes this month. What Barcelona's immediate opponents, Celtic, may well discover, to their distress and wonder, is that Messi is not only the most naturally gifted dribbler in the game today, he is an increasingly menacing scorer of beautiful goals.

All professional footballers, with the possible exception of goalkeepers, score one memorable goal in their careers. The top forwards, if they are lucky, will score a goal that will go down in history. The thing about Messi is that, while he still has his whole career ahead of him, he seems to score a great goal every couple of weeks and he has scored three in the past year that will endure as works of art.

The first goal, extraordinary both because of the circumstances of the game and the quality of the execution, was in the Spanish superclásico for Barcelona against Real Madrid at the Camp Nou in March last year. It was the last minute of the game and Barça, who were down to 10 men, were losing 3-2. Messi received the ball on the edge of the Real penalty area, inside the semi-circle. There was nothing on. The entire Real team were behind the ball; their only purpose now to stop Barça scoring. Messi veered left, shifted up a gear and accelerated past a couple of Real players, whom he left sprawling on the floor, and entered the area.

Leo, as he is known, still had Sergio Ramos, Spain's best defender, and Iker Casillas, the world's best goalkeeper, to beat. He sailed past Ramos, who also fell at his feet, blown aside by his sheer speed, and he cracked the ball with his left foot into the corner of the net, shaving the inside of the post, leaving Casillas with no possibility of reaching it. It all happened in the blink of an eye: the goal that gave Barça a point, Messi's third in a 3-3 draw that, in the eyes of the hundreds of million watching the game that night, anointed the young Argentinian as the latest football divinity, a player destined to delight the football world.

That was the first dish of the three-course Messi menu - tasty, digestible, light. The second goal, a month later, was pure Pampas protein. This goal against Getafe in the Spanish Cup replicated, step by uncanny step, the greatest goal of all time, Diego Maradona's second against England in Argentina's 1986 World Cup quarter-final. After receiving the ball wide on the left of the halfway line, he dribbled past the entire rival defence before scoring.

The third goal, an airy mousse dessert, was in June against Mexico for Argentina in the Copa America. This one required only two touches. With the first, he controlled the ball at full speed on the left-hand corner of the Mexico penalty area; the second, still at speed, a quite sublime lob. The entire stadium, goalkeeper Oswaldo Sánchez and defender Rafa Márquez not excluded, expected either a low shot or a cross inside to Carlos Tévez, who was in a good position to score. What Messi did, instead, was to apply the finest of touches to the ball with the tip of his left boot in such a way that the ball traced a perfect arc, unstoppable, geometrically faultless, brushing the underside of the bar in its floating course - as if steered by a passing breeze - towards the back of net. It was pure instinct, pure genius or, as the Sky TV commentator put it, 'That is perfection!' The connection between Messi's brain and boot at the very instant when his legs reached their peak of acceleration was an anthem to the wondrous biological complexity of the human animal.

In person, dressed in regular civilian clothes, off the field, without a ball in sight, Lionel Andrés Messi is not wondrous at all. He is stunningly ordinary. Pale-skinned, thin-lipped and shortish - though the shoulders do show the sinuous evidence of toil at the gym - he turned up for our interview at an anonymous room somewhere in the bowels of the Camp Nou, Barcelona's giant stadium, dressed in a short-sleeved yellow shirt that he might have borrowed from his dad, blue jeans and white running shoes. No body piercings or tattoos in sight, and a lank head of hair no stylist's fingers have touched, Messi is the anti-Beckham. He is not a sex symbol; he is a football symbol. On the pitch he is a god; off it, he is one kid more from Rosario, the unglamorous industrial town 200 miles north-west of Buenos Aires where he was born and raised.

How does one get to be so good? I asked him for an interview I did with him recently for Sports Illustrated Latino, the Spanish-language version of the celebrated American magazine, after they had selected him Latin America's best sportsman of 2007. 'Well,' he replied, with an Argentinian accent, as distinctive as Australian in English, that seven years in Barcelona have modified not a jot, 'first of all you've got to love the game.' How much? 'Well ... from the age of three I played every day: every morning, afternoon and night. Inside the house, too. I'd break things. My mum would go mad ...' Does he still play inside the house? 'I do,' he said, with a sliver of a shy smile. (Messi is not the happy, slappy Ronaldinho type; his face only bursts with joy when he scores a goal.) 'Yes, I'm still like that. At home, wherever, I have to have a ball nearby. I have to be able to touch it.' Caress it, as Brazilian footballers say, as if it were a woman? Messi nodded, but he looked away, so that I could not see his smile.

Apart from a love for the game, what you need to succeed, Messi said, is a lot of work and sacrifice. Sacrifice? I said. Sacrifice, when they are paying you a fortune to do what you like most? He stirred out of his timid semi-torpor for the first and only time in the interview, betraying a hint of what might have been indignation. 'Yes, sacrifice. When I was 13 I left Argentina. I left my friends and most of my family and I came to Barcelona. Even though my parents came with me, it was hard at that age.' It was also necessary. Messi is no beefcake but he would have been even shorter and thinner - more 'flea' - if it had not been for the growth hormones that FC Barcelona paid for him to have, and that neither his family nor his Rosario club, Newell's Old Boys, could afford.

Messi turned up at Barcelona's youth training ground for the first time at the end of 2000. Within five minutes Carles Rexach, a former Barça player and coach, announced: 'We'll have him.' Aged 13, he had the physique of a boy of 10, but a blazing talent that he was able to develop and consolidate thanks to plenty of that hard work he spoke of, and to daily hormone injections. He grew to an acceptable size and rocketed through the youth ranks, making his first-team debut as a substitute at the age of 16.

'The Barcelona youth programme is one of the best in the world,' said Messi (an irrefutable point given that, in recent years alone, it has produced players of the quality of Andrés Iniesta, Xavi Hernandez and - of course - Cesc Fábregas). What was the secret? 'As a kid they teach you not to play to win, so much as to grow in ability as a player. That's why, in contrast to the experience I'd had in Argentina, where it was all much more physical, at Barça we trained every day with the ball. I hardly ever ran without a ball at my feet. It was a form of training aimed very clearly at developing your skills.'

Barça's investment started to pay off in the 2004 pre-season when, aged 17, he made his first start at the Camp Nou in a friendly against Juventus. 'That,' said Messi, with a rare hint of pride, 'was the day in which people got to know who I was.' Dead right. Everyone who watched that game, packed as it was with world-famous players on both sides, knew that Messi was going to be something special. Capello, then manager of the Italian side, added his own gruff words of praise. 'Where did that diavolo come from?' he asked.

Bernd Schuster, the present manager of Real Madrid, sees Messi as an untameable animal. The former West Germany international, Getafe's manager when Messi scored that remarkable goal last season, hurled an indirect piece of flattery the Argentinian's way when he said: 'I'll have to put my dog's collar on him to see if I can calm him down a bit.'

If David Beckham were a dog, the problem would not be so much the collar as how to brush his hair. The Englishman, whose global fame is out of kilter with his talent, is a naturally super-fit individual who, through perseverance and repetition, evolved into a great dead-ball player. Messi is a great live-ball player. He is a natural-born footballer, the genius of the school kickabout game, fast and ultra-gifted at the elemental art of taking on a rival and beating him. Even Ronaldinho, his brilliant but lately fading team-mate, is a more studied kind of player; one who thoughtfully, deliberately 'imagines' a sequence of play in his mind, as he told me once, the night before a game. Messi is spontaneity itself. 'I don't watch games I've played in on TV. They say you should to improve your game, correct your mistakes. But I don't,' he said. Neither does he take much interest in other players. He confessed to a certain weakness for his compatriot Pablo Aimar, who also plays in Spain, 'but I don't try to imitate anybody; I play the way I feel'.

That is maybe why his team-mates are as baffled as his opponents as to what may happen next when he is on the ball. Gabriel Milito, who knows him well from both Barcelona and the Argentina national team, said he had stopped being surprised at what Messi can do. 'Each game he plays, you rub your eyes and ask yourself, "How did he manage that?" You begin a game wondering, "What will Messi do this time?"' Milito, who plays at centre-back, first came across Messi in Argentina. 'At our first training session with the national team I knew he was quite different from every other player. I have played with huge footballers, but none like Leo.'

Those are strong words. Milito plays for Argentina alongside players such as Juan Román Riquelme and Carlos Tévez; at his club, with the so-called 'four fantásticos'. Messi himself is one of them; the others are Ronaldinho, Eto'o and Thierry Henry. But even they are aghast at the talent of their young colleague. It was Eto'o who compared Messi to watching cartoons. Henry has confessed that he runs the risk, while on the same field of play as Messi, of becoming a spectator. 'What he does is so incredible I have to be careful not to stand still watching him make his moves.' Ronaldinho is extremely familiar with his Brazilian compatriot Kaká, the freshly crowned European and world footballer of the year, but he said in November, before the results were in, that if he had a vote it would go to Messi, a player whose 'evolution' he said he had followed with 'wonder and awe'.

Ronaldinho is right. Messi's evolution has been astonishingly fast. First because he has emerged in the past 12 months more and more as a scorer, not just as a creator, of goals. Since that hat-trick against Real Madrid last March he has scored an average of just under a goal a game. Second, to that unique dribbling ability of his he is adding a speed of thought and vision of the game from which Ronaldinho himself has drawn benefit. If one examines the flickers of brilliance that still flash occasionally from the Brazilian's boots, one sees that they tend almost always to be the result of an electric interchange with Messi: one-twos or, something you see in Messi more frequently as he matures, a perfectly weighted laser pass, not unlike those Maradona would make, that creates a chance of a goal.

It is hard to tell what fame and money might end up doing to a young man from a humble background, but so far the indications with Leo Messi are that he will not fall apart, after first imagining himself to be God, the way Maradona did. The very opposite of flashy, he does not opine on anything and everything the way el Diego did - and still does - and, indeed, it is quite clear that he does not feel comfortable talking to the media, that he would pay good money to be spared the discomfort of press conferences and interviews. Happiness for Messi would consist of being left well alone to let his feet do the talking.

Whether he will ever be as good as Maradona or more to the point - for he is quite possibly as good already in terms of sheer ball skills - whether he will ever acquire the same commanding presence on the field, one cannot yet tell. What is clear, though, is that he is on his way. Messi is already considered both by the players and by the fans to be Barcelona's leader on the field. He has ceased being what he was at 17 and 18, the lone ranger of the right wing, to become, two years on, Barça's undisputed sheriff. He inspires the rest with his runs and with his first-line-of-defence tackling; he creates goals and scores them. He has a hummingbird quality that defines the movement and pace of this Barcelona team at their best.

They have not been at their best this season. Ronaldinho looks weary, sated, fat. Henry has had to deal with injury plus the inevitable difficulty of adapting to a new team. Eto'o has been out injured most of the season. All of this has meant that a less talented but more cohesive and driven Real Madrid team have been ahead of them in the league since September, consolidating their lead after beating Barça 1-0 at the Camp Nou in December, thanks in part to Messi's badly timed absence through injury.

But with Messi returning to the team this month, there are worrying - at least for Celtic - signs of recovery. Henry is blending in better and recovering some of the spark and power he had at Arsenal, while Eto'o is back from injury looking hungry and lethal. An extremely exciting young player, 17-year-old Bojan Krkic (see panel on page 23), is emerging as a more than adequate replacement for Ronaldinho. There is also the possibility that Ronaldinho himself may take flight again, as swiftly and inexplicably as he faded. With all these options, plus some mightily impressive players in defence and midfield, Barcelona remain the team with the most brilliant potential in Europe and probably, even on a less-than-perfect day, the best to watch.

About half of that is down to Messi who, at his best, is amply worth the price of admission on his own. He seems to know it yet he remains, as he probably always will, low-key, humble - qualities he must preserve if he is to become acknowledged as not only the best player of his generation, but as a historical rival to his great predecessors at Barça, Johan Cruyff and Maradona. 'I still have a lot of room for improvement,' he said. 'For example, shoot equally well with both feet. I still have work to do on my right. I could also do with learning how to take free-kicks like Ronnie [Ronaldinho].' But does he aspire to be unanimously considered the best in the world? 'Well ... it would be nice, but it's not an obsession. More than anything else I dwell on how lucky I am. Every day I thank God for all I have been given, and for the luck I've had in being able to play alongside these fantastic team-mates of mine both in Barcelona and Argentina.'

Messi may rest assured that they say the same, only with more feeling, about him.

The new Ronaldinho

The most sensational young player in Spanish football this season, Bojan Krkic is the latest jewel to emerge from the Barcelona youth programme. The son of a Serbian footballer (Bojan Snr, now a Barça scout, played for Red Star Belgrade in the Eighties) and a Catalan nurse, he scored 889 goals in seven years in the Barça youth team before making his senior debut during pre-season in 2007, aged 16. Unfazed by his fantástico team-mates, he caught the eye not only with his skill but with his impudent self-confidence, trying tricks as audacious as Ronaldinho's, shooting with the abandon of Samuel Eto'o.

Bojan turned 17 in August and has played in more than 25 first-team games. At 5ft 6½in, he bears a distinct physical resemblance to Michael Owen. He is a more rounded talent than Owen; soon we will know whether he lives up to his promise as a prolific goalscorer.