Early afternoon at a photographic studio tucked away in sleepy suburban Surrey, a stone’s throw from the Thames, and Diego Costa is intent upon keeping himself busy. The Chelsea striker is playing the outcast at present. He has trained back at Cobham with his customary gusto, an attempt to avoid being blunted by suspension, and has crammed commitments with sponsors into his schedule to occupy his time, but the three-game ban that condemned him to the periphery has clearly left him as bored as he is exasperated. His return at Paris Saint-Germain next Tuesday night cannot come soon enough.

The last few weeks have been spent marooned on the sidelines, sitting in the East Stand alongside a hamstrung Cesc Fàbregas when Manchester City visited Stamford Bridge at the end of last month, absent altogether at Villa Park, and back between the masseurs twiddling their thumbs behind the home dugout when Everton were narrowly beaten in midweek. “It is frustrating not being able to play because I cannot help my team-mates out on the pitch,” he admits. “If the game is hard out there, really tight as they have been, I sit there kicking every ball. Being very active. I get very caught up in it. I can only watch calmly if the match is decided or my team are dominating. But I get passionate very easily.” Those substitutes sitting directly in front of the forward, a bag of nerves as he thumped the Perspex barrier through the dying moments of Wednesday’s tight win, would vouch for that commitment.

The impartial might argue that Costa brought all this upon himself. Had he not planted his right foot on to Emre Can’s shin near the touchline early in Chelsea’s Capital One Cup semi-final second-leg victory over Liverpool – contact that was deemed deliberate when viewed retrospectively by the referee, Michael Oliver, and then assessed by an independent regulatory commission after the player had contested the Football Association’s violent conduct charge – there would have been no suspension to serve. His manager has regularly disagreed, outraged as he still is by the focus the incident has drawn. The striker feels he has said enough on the subject. His stance has not changed, his insistence of innocence maintained.

The contact was clumsy rather than malicious – “not on purpose, just look at the video”. As far as he is concerned his conscience is clear. There is no reason to change his approach. When he returns to action in the Champions League he will be as aggressive as ever, intent upon unnerving Thiago Silva and David Luiz in the heart of the Parisian defence in just the same way as he muscled into Vincent Kompany and Pablo Zabaleta at Manchester City, and Martin Skrtel and Mamadou Sakho at Liverpool earlier this season. Or even John Terry when Atlético Madrid prevailed at Stamford Bridge in last April’s semi-final, an occasion swung by what remains his most recent goal in European competition. A competitive spirit takes over and always will. He admits that, on the pitch, “I transform myself”. Without that ferocity he would not be the same player who boasts 17 goals from 19 Premier League appearances.

Facebook Twitter Pinterest Diego Costa flicks the ball past West Bromwich Albion’s Ben Foster. Photograph: Tom Dulat/Getty Images

There will inevitably be ramifications from the Can affair, whether that means even greater scrutiny from referees and pundits, or more eagerness from opponents to make the most of any contact. Logic suggests he may find himself provoked. “But I’ve been a target for defenders for a long time, and I am used to getting kicked by them, to get knocked by them,” he says, the response drawing a nod of approval from the entourage of agents hovering on the fringe of the interview.

“I know all about that already. I also fight and tackle, even if some defenders complain at the slightest contact. To me, you draw a line under all that as soon as the game is over. We shake hands and it is all [left] on the field. I think the referees should think about how many times I am hit or kicked before I get angry about it. But referees here in England are good enough and professional, and they also understand well and realise what happens out on the pitch. They take that into account.

“I don’t go into a game with specific targets. I don’t pinpoint an opposing player before a match, trying to exploit a kind of weakness. If you pinpointed someone before the kick-off, probably you would become embroiled in a fight and you would be distracted from what really matters and not play well. When you are going in to a game to confront Thiago Silva and David Luiz, you can’t modify your way of playing. They are both great players, great defenders, in a great PSG team. I may argue with them on the pitch, there may be contact, but that is not a plan. That is the emotion. The battle. Forget about specific plans. My only goal is to score, and to play as well as I can for my team. All I can do is try and be in the best possible shape.”

Last season Costa was La Liga’s most fouled player, ahead of Cristiano Ronaldo and Lionel Messi. Team-mates rejoice in his rugged refusal to wilt, using it as a sense of inspiration as well as reassurance. He had endured regular ugly run-ins with Real Madrid’s Sergio Ramos at the Vicente Calderón and Bernabéu, but it was the defender who persuaded the Brazilian to adopt Spanish nationality.

It transpires that talk of Costa approaching Terry before the opening game of the season, at Burnley, to seek assurances the captain would back up the striker’s approach – “I go to the limit” – is nothing more than an urban myth, but that scenario still feels eminently plausible. There may be the odd ban to endure along the way, but his team-mates recognise the 26-year-old is an asset.

The raw aggression is a reflection of a career struggling to clamber up the football ladder. It is that of a player toughened on the streets of his home town, Lagarto in Brazil’s Sergipe state, rather than a European superclub’s plush academy, and an upbringing that took him from his parents, at 14, to São Paulo over 2,000km away ostensibly to help on his cousins’ market stall selling clothes. There he lived with his uncle, Edson, who offered work in his own store, frequented by local coaches, and the youngster duly forged a reputation at Barcelona Esportivo Capela, a club in the favela in the south of the city. He earned £100 a month and made an immediate impression by flooring the team’s most promising defender, Felipe, in his first training session.

Costa had his first taste of the “professional” game at Barcelona EC, impressing in the youth setup, though prospective moves to the junior teams at Portuguesa, São Paulo and Palmeiras came to nothing. Then a scout working for the agent Jorge Mendes saw him play in the flesh as an 18-year-old, albeit only after Barcelona EC had successfully petitioned for the striker’s 120-day suspension for punching an opponent to be revoked after arguing he had been provoked. A lonely, nomadic existence in Europe, where Mendes initially placed him at Braga, featured loan spells with five teams in Spain and Portugal and four permanent moves in as many years. That period was unsettling, prompting periods of self-doubt, but there was enough promise in the brief glimpses he offered to persuade Atlético to purchase him twice – from Braga in 2007 and back from Valladolid three years later – and the player’s motivation to succeed was relentless.

Diego Costa: ‘Football is my life.’ Photograph: adidas

“Football is my life and I cannot imagine myself doing anything other than playing this game,” he says. “I’ve been through a lot to get here and I know now the difficult thing is to maintain myself at this level. To stay here and to maintain yourself among the best you have to become a better player and a better person as well. So I have to work and improve as if there was no tomorrow. Obviously I have to enjoy all I have. People depend on you, and now I can look back at everything I’ve gone through to get here with a different perspective. I am glad I have given my family the life I wanted for them. That is my responsibility.”

He has done more than that. Back in Lagarto, an unremarkable town of red-bricked houses and around 100,000 people in the inland savannah in north-east Brazil, he funds Bola de Ouro, a non-profit football “academy” which has already become the pride of the region. He had attended as a child when it comprised of a field scarred by a thoroughfare, training drills often interrupted as farm vehicles trundled across the turf.

Now, while the academy is a work in progress, the setup is transformed: relocated in grounds next to the area’s tobacco plantations, with proper equipment, organisation and structure. More facilities are to be added to the medical centre, classrooms and three outdoor pitches currently being used by around 230 local boys up to the age of 17, but the revamp is already making a positive impact on the region.

While much of Brazil vented their spleen at Costa when he strode out in Salvador at last summer’s World Cup with La Furia Roja for his adopted nation’s opening group game against Holland, Lagarto’s main square was crammed with locals clad in replica Spain shirts for the day. He is cherished. “I look back and I know what I left behind in Lagarto when I pursued my own dream,” he says. “I started the project with the help of my agent, who represents some of the finest players in the world, in the hope it would help open doors for some of the kids back home. The children there will get the chance I never had. They will live close to their parents, staying away from drugs and off the streets, and have proper guidance in good surroundings in the town. It can only bring positive things to the area.

“Lagarto is a small town with very few opportunities for kids who want to be footballers, so this gives them a chance. We have great professionals working there, which is the key to all this. The structure is still growing, but there are better football pitches and things I didn’t have access to when I lived there, such as food, good medication, and support. There is nothing missing in there. The teachers and coaches are always happy to help if a kid is going through a rough time. The main target of the academy is education, rather than producing professional footballers, and attending classes is mandatory. If a kid skives a lesson he won’t be allowed to attend a training session. Some of the children may not become footballers, but they will all definitely be better people for attending the academy. There is more to gain than lose.”

The desire to establish a legacy is noble, a contrast with the depiction of Costa as the wild-eyed battering ram impervious to pain. The man who once cut his leg to the bone after colliding with a post to convert a rebound against Getafe, prompting his then manager, Diego Simeone, to sympathise with the woodwork. “Another cut doesn’t harm the tiger,” said the Atlético manager. “Anyway, it’s the post I feel sorry for.” His game progressed markedly when given his opportunity, once Sergio Agüero, Radamel Falcao and Diego Forlán had moved on. There were 56 goals in two seasons. Chelsea invested £32m in proven pedigree.

“I was already improving a lot during my spell at Atlético, but I’ve always sought to improve personally year on year and it’s really important to have a mentor who guides you,” he adds. “José Mourinho has been really clear about what he expects from me, saying he wants me working hard rather than just scoring. Hard work is what he values. Up to now, things have gone phenomenally well for me at Chelsea.

“There is a great sense of unity in the squad, similar to what we had at Atlético last season [when the team won La Liga and reached the Champions League final]. We all want the same thing, and we all have the same work ethic. You need that to be successful as a group. It has helped me having players like Cesc here, someone I knew [from Spain] but also a player who reads my movements and provides me with so many opportunities. He has a real gift for passing.” The pair have already struck up a near telepathic relationship out on the pitch, but the ease with which Costa has adapted to English football has still taken the breath away.

He will plunge himself back into the fray next week, when PSG and then Burnley are likely to bear the brunt of his frustration after three weeks on the sidelines. Costa will return unchanged for that experience, but more eager than ever to make his mark. One of the Chelsea backroom staff, albeit sporting a mischievous smile at the time, recently described him as a “saint”. How would he describe himself? “Yes, I’ll go with that. Call me a saint.”