In the summer of 2007, having just arrived at Atlético Madrid, Diego Costa was sent to the club’s summer training camp, just another young player honing his football skills. For Costa, though, this would be the first of many summers sweating in the rojiblanca jersey.

His presentation to the media on 10 July was memorable for two reasons. Firstly, the club’s president, Enrique Cerezo, boldly declared they had signed “the new Kaká” and the club took the unusual step of providing the media, who at that time knew little or nothing about the player, with a surprise extra in the official press pack. A journalist, Sergio Perela, who was at the event, explains: “He was such an unknown that as well as the usual press pack, they gave us a DVD showing some footage of him playing.”

That morning, speaking in a Portuguese not dissimilar to the Spanish he speaks today, Costa described himself as a “second striker, with a good burst of pace” and assured the packed VIP suite in the Vicente Calderón stadium that he had always dreamed of “playing for a great club like this” and hoped to prove to them “just what I’m made of”.

Atlético’s pre-season had kicked off the day before the press conference, on 9 July,when they played Manzanares. Ahead lay the qualifying ties of the Intertoto Cup, which would be their ticket into the Uefa Cup. It would prove a bumpy ride. A solitary goal from Atlético’s Diego Forlán in the second leg of the third round was needed to take them past Gloria Bistrita of Romania, on away goals. Costa, however, took no part in these early stages of Atlético’s European campaign.

“Costa had just come back from his injury and he used to come to training with his laces undone,” reflects García Pitarch, Atlético’s director of football, on the Brazilian’s early days in Spain.

“He also tended to be at the back of the pack whenever the squad was doing laps and clearly preferred to stick to the inside lane, where you end up covering a shorter distance. The first team coach, Javier Aguirre, came to see me one day and had a bit of a moan. ‘That lad’s a real pain in the arse and the sooner you loan him out and get him out of my hair, the better. He’s a disaster who runs around with his shoelaces undone.’

“I’m afraid I was a bit short with him. I said, ‘Javier, that’s what you’re here for – to teach him how to do things right. I bet it hasn’t even occurred to you he keeps his shoelaces undone because he’s just come back from a six-month injury and he’s still in pain. And maybe he takes the inside lane because he doesn’t know any better. It’s your job to educate the lad and explain this stuff to him. Don’t just assume he knows what he should be doing. We’re not talking about a 30-year-old pro here. This is an 18-year-old kid who is still learning.’

“Then two weeks later Javier comes back to me and says: ‘You were right. I had a chat with him and he’s taken it all on board. I’m delighted.’ Sometimes you have to give young players a bit of extra help to stop them messing up.”

It was decided Costa would be loaned out to Celta Vigo. “We all got together in the Goizeko restaurant in Madrid’s Wellington Hotel – Ramón Martínez, Manuel García Quilón, Miguel Ángel Gil Marín and I,” Pitarch recalls. “And we agreed to loan them Mario Suárez and Diego Costa. I told Ramón Martínez [at Celta] straight out they would need to keep on top of Diego because he still needed to learn how to behave like a professional. He had practically no club experience and didn’t really understand the code of conduct we expect in the dressing room. He was pretty much an ingénue in all of that. I told him: ‘If you leave him to his own devices it will be a disaster. It’ll cost you financially and deprive me of a potentially great player’.”

Costa was still an unknown quantity when he arrived at Vigo. “I had just come back from injury and people were perhaps not expecting a lot from me,” he says. Roberto Lago, who had just broken into the Celta first team, agrees. “None of us had heard of him when he arrived and we were all pretty surprised when he turned out to be such a good player.”

Diego Costa played 30 times for Celta Vigo, scoring five times, in 2007-08. Photograph: David/Offside - MarcaMedia

Ramón Martínez says: “We were delighted with his football from day one. That was when we started to believe that we had the squad we needed to move up.” Unfortunately Celta’s high hopes would, in the end, be dashed. Several of the squad which had crashed out of the Primera Division the previous season had remained with the club, including the manager Hristo Stoichkov, who had been rushed in to replace the unfortunate Fernando Vázquez towards the end of the disastrous 2006-07 campaign.

Costa’s game has since been compared to that of the feisty Bulgarian in his pomp, and he soon became a regular in the teams selected by the 1994 Ballon d’Or winner. The Brazilian, in white boots and rolled down socks over shin guards cut down especially by the Celta kit men, was soon scoring goals for his new side. He also quickly became the centre of attention for other, less laudable reasons.

In their seventh league match, Celta played Xerez at home and were dominating the match. Costa got his first goal in Spanish league football, diving into the six-yard box to finish with 15 minutes left. He raised his hands to the sky in a gesture that spoke as much of sheer relief as any religious devotion. But his celebration did not end there. His Celta team-mate Jesús Perera described it: “I remember he went to the corner and started fooling around with the ball, prancing about like a bull fighter.”

The Xerez players were quick to react and Costa, never one to back down from a confrontation, responded by laughing at them. All hell broke loose. Agus, a Celta defender that day, recalls: “Antoñito [a striker for Xerez] in particular took it badly but Brazilians can be like that and I don’t think he really intended to offend anyone.”

“He didn’t play in the return game at Xerez,” adds Fernando Sales, then of Celta. “It was just as well because no one there had forgotten him. We did explain to him after the match that you can’t behave like that in Spain.”

The referee showed Costa a yellow card, his second of the match, for his first sending-off since arriving in Spain. He apologised at the press conference later. “I messed up and I’m sorry. I know I shouldn’t have done it, but it was just a spur of the moment thing. It won’t happen again.”

When asked about rumours of more trouble in the tunnel after the match, Costa denied involvement in any incident but confirmed that, had anything happened, he most certainly would have been a part of it. “Nothing happened afterwards. You know, I’m no coward. I’m a man and I’m not scared of anything.” His public apology did not save him from his manager’s rebuke. “Stoichkov went absolutely apeshit,” remembers his team-mate Antonio Núñez.

Diego Costa in action for Celta Vigo. Photograph: L pez Perujo/EFE/Press Association Images

Within days the Bulgarian had decided to resign, citing personal reasons. “I was waiting for a good result before I made the decision to leave,” explained Stoichkov. The news came as less of a surprise to everyone inside the club, where it was an open secret that assistant coach Antonio López had been taking all strategic and tactical decisions. Hristo packed his bags and was replaced by Juan Ramón López Caro.

Costa was faced with the challenge of adapting to life in a new city whilst maintaining a strong performance on the pitch. His main ally in this was Eugenio González, known as “Bosman” at the club because of his role in settling in foreign players. “We got on like a house on fire from the start and I was happy to help him find a place of his own,” recalls González.

“I remember how passionate he was about football. Training wasn’t enough for him and he used to play with his mates on the university pitches at 11pm. I said to him, ‘Diego, you can’t keep doing that. You’re going to do yourself an injury’. But he couldn’t help himself. Football was his life and he was either playing it himself or watching the Brazilian league on television.”

As it turned out, Bosman was wrong and the young Brazilian continued to enjoy his late night sorties under the Galician stars with no ill effect. Meanwhile, his game was winning Costa legions of fans. “Diego Costa, the new Celta sensation is more than ready for Sporting,” declared the Faro de Vigo newspaper before a visit to Real Sporting, which ended with him scoring the winning goal.

His new coach, Juan Ramón López Caro, was quick to see Costa’s potential but also had to endure the player’s idiosyncratic behaviour. During their 16th league game, against Sevilla Atlético, he was booked first for diving and then, 19 minutes later, for his almost continual protests at the referee’s decisions. Down to 10 men, Celta fought back from a goal down to draw, but the atmosphere in the Balaídos stadium had shifted. The fans who had applauded him as he left the pitch after his first red card were now murmuring in disapproval.

Costa’s appearances were frequently marred by disputes. The previous week, away at Málaga, he kneed the defender, Weligton, in the head, causing an injury which required six stitches. After the match, Weligton revealed this had not been his first experience of Costa, whom he had encountered in his League of Honour days with Penafiel in the Portuguese second division and warned referees they should keep an eye on the player.

Costa responded in no uncertain terms: “I wasn’t out to injure him but he was kicking me, Contreras and Quincy all over the pitch the whole game. He and their goalie were way over the top in their tackles on me but, just because I didn’t end up bleeding, no one’s talking about that. I don’t need to hit people in order to play good football. I’m not a boxer after all. But Weligton is happy to throw a few punches himself. It’s just that he’s dishonest about it. I don’t know what he’s snivelling about anyway. He’s such a big girl. Maybe he should take up volleyball instead.”

The next day the Málaga press led with: “Diego Costa raises hell in the second division.” In all likelihood the striker was more irritated by the hard tackles on the Dutchman, Quincy Owusu-Abeyie, who was his best friend at the time. “They were always together,” recalls Núñez. “The rest of us couldn’t understand how they communicated, because one of them could only speak Portuguese and the other stuck to English all the time.”

Team-mate Roberto Lago explains: “Diego told me how they did it: ‘I don’t speak English so we use sign language instead.’ We were actually worried that he would be led astray by Quincy, who was a bit of a rebel.” Ramón Martínez echoes this sentiment: “Quincy was a phenomenal player but totally unmanageable.”

Later in the season, the Celta board made Alejandro Menéndez, the youth team coach, the manager of the first team and their fourth of the season. He did not use Costa much, preferring to put the team’s fate in the hands of more experienced players. In the one match Costa did start, the striker earned his third red card of the season. His reaction took the coach aback.

Menéndez takes up the story: “We were playing Tenerife in Balaídos and were winning 2-0 in the 20th minute, by which time he had already got himself a yellow card. Then, as we tried to take a quick free-kick, Costa hauled an opponent away from the ball, got a second yellow and left us with 10 men. We ended up with a 2-2 draw and in the dressing room after the game he came up to me and with that almost childlike frankness of his said: ‘Mister, please forgive me. I’m still young and I know I have a lot to learn.’

“I was surprised and impressed that a player had the guts and honesty to recognise that he had messed up and damaged the team’s chances. It was the same with training. If he turned up late, he wouldn’t give you a load of bullshit. There would be none of the usual, ‘the alarm didn’t go off’ rubbish. He would be totally upfront and tell me he’d been up most of the night playing PlayStation. It made me really warm to him.”

Arena Sport Photograph: Arena Sport

Costa also apologised to the public: “This has taught me a hard lesson. I have to learn from it. I have to change. I have no idea why these things keep happening to me,” he said, his head bowed. Celta finished the season having saved themselves by the skin of their teeth, not much recompense for a team which had started the season with high hopes. “People ended up not thinking much of me. They saw me as a bit of a troublemaker,” reflected Costa. “It’s important to change people’s impressions. I always commit myself to the teams I play for and always want to win. I hate losing. It’s just that at times I go about things the wrong way and that created problems.”

His relationship with the fans had been bittersweet. Despite the fact he and the Uruguayan, Fabián Canobbio, were almost unanimously seen as the two best players in the squad, the fans disliked what they saw as his constant dissent on the pitch and his tendency to want too much time on the ball.

“He could lose it too easily back then, although in some of those games the referees and opposition players were kind of waiting to see if they could provoke him,” says Núñez.

“It was clear he was headed for bigger things,” adds Agus. “You could see in him things that most players don’t have. I loved how he played with his back to goal, held it up against even the toughest defence and then turned to run at goal with such ease. And he didn’t care who he went up against – whether it was an older, more experienced player or not. There are some strikers who back down if you give them a bit of a shove, but not him. He would keep coming no matter how much you kicked him. His development has been very similar to that of Álvaro Negredo, whom I’ve also played with. They have both worked to perfect their game and are now brilliant strikers.”

“He had almost everything you need to make a great forward,” Esteban Suárez, a Vigo team-mate, adds. “You could see how talented he was back then, although he wasn’t as good as he is now. He was brilliant up front and what really struck me was how well he played under pressure.”

Canobbio adds: “Perhaps back then it was his finishing he had to work on most.”

“Of all the players I’ve worked with he’s the one who can get away from three players in the tightest of spaces without any need to look particularly elegant doing it,” explains Lago. “There were games when he was out of sight. And he was amazing in training.”

His Celta team-mates are unanimous about Costa the man. Super-competitive and nasty on the park, off it he was the opposite. After overcoming initial shyness and the language barrier, the striker became a larger‑than‑life presence around the club. “He always arrived in his car with the music at full volume,” says Agus. “Always singing and dancing,” adds Fernando Sales.

Looking back at those early years, Costa said: “I grew up thinking a bit of pushing and shoving was completely normal. Then I suddenly learned that if you kick another player, you get in trouble. Nobody had ever reprimanded me for that before.”

Extracted from Diego Costa: The Art of War, by Fran Guillén, published by Arena Sport at £9.99