Andrés Iniesta says he heard the silence and knew that all he had to do was wait for Isaac Newton. The ball sat up; gravity would bring it down again and, when it did, he would score. It was the 116th minute in Johannesburg and he did score, running to the corner and pulling off his shirt to reveal the message underneath, written in blue marker by Hugo the kit man: “Dani Jarque, always with us”. Ten thousand miles away Spain erupted and Jessica cried. Through the tears she saw it: Dani, her Dani.

The 2010 World Cup final was the first game Jessica had watched since her husband had died 11 months earlier, aged 26. She watched on television with her mother, María, and daughter, Martina, 10 months, as the ball sat up. What followed was more than just a goal, Iniesta reveals – for all of them. It is sunny in Sant Joan Despí as, six years on, he explains how that moment pulled him from “a dark place”.

Iniesta might not have been there then and without that goal he does not know where he would be now. Perhaps not here at Barcelona’s training ground, one of the world’s most celebrated footballers. Late on the night before the final, with everyone asleep, he quietly opened the door and, without leaving the hotel, set off for a run. Down the corridors he sprinted until he believed he could do this. All tournament the physios, working past 4am, had promised he would be OK even when they thought he would not be. Now, he was – vulnerable but ready.

This was more than Iniesta’s muscles, though; it was his mind. The security of waiting for Newton masked the insecurity and suffering of the months before. In 2009 he won the European Cup and the following summer the World Cup. It should have been the best year of his life; instead it was the hardest. Between the two titles he suffered. “Not depression exactly, not illness either, not really, but an unease,” he says in his book, The Artist, published today. “It was like nothing was right.”

André Iniesta celebrates scoring the winning goal in the 2010 World Cup final against Holland. Photograph: Jamie McDonald/Getty Images

Iniesta had played the 2009 final injured, warned not to shoot. In pre-season, still not fit, Carles Puyol delivered news: his friend Jarque, captain of Espanyol, had died. The impact was profound, body and mind suffering together. Tests showed nothing specific physically but Iniesta could not complete sessions, Pep Guardiola telling him to walk whenever he needed, which he did often. They would wait, Guardiola said, and the wait went on. When Iniesta played he was not the same and April brought another injury. The World Cup, the light he sought, risked being extinguished.

Iniesta says he had felt as if he was in “freefall”. Unable to go on, he turned to the club’s doctors, seeking professional psychological treatment. If doing so can carry a stigma, especially in sport, he says: “When you need help, you have to look for it: at times it’s necessary. People are specialists; that’s what they’re there for. You have to use them.”

I understood that I was enduring a delicate moment but I took refuge in my people and, above all, in football

So Iniesta did – quietly, privately. He needed help; he talks about being “on edge”, “vulnerable”, “victim of something that terrified me”. Team-mates did not know. Nor had he said anything publicly. There is a kind of catharsis, or perhaps a closure, in doing so now. He had talked about Newton before but not what lay beneath, how significant that moment was. What would have become of him without it? What if Spain had not won the World Cup? It is not a glib question.

Despite his reluctance to define what he suffered as “depression”, there is a passage in his book where Iniesta writes that he can “understand” how people end up committing a “locura”: how they can end up doing something “crazy”, an act of “madness”. What does he mean? In the context it is a powerful word, frightening and uncomfortable: mental health can be delicate, the desperation debilitating and the consequences dreadful.

“When you’re not right, you experience moments that impact upon you, that worry you,” Iniesta says. His words – te imponen respeto – defy simplistic translation but imply fear, a sense of the situation being bigger than you, beyond you, not entirely under control. “Those are difficult, uncomfortable moments [but] to go from there to certain extremes,” he says, “… well, every case has its peculiarities…”

“There are moments when your mind is very vulnerable. You feel a lot of doubts. Every person is different, every case. What I’m trying to explain is that you can go from being in good shape to being in a bad way very quickly.

“I never reached the point of saying: ‘I’m giving up.’ I understood that I was enduring a delicate moment but I took refuge in my people and, above all, in football. I never felt I didn’t want to continue playing. I knew one day I’d take a step forward, maybe the next it would be three, then five … it’s a process and that’s how you overcome it.

Andrés Iniesta celebrates after Barcelona’s 2-0 triumph against Manchester United in the 2009 Champions League final. Photograph: Claudio Villa/Getty Images

“People see footballers as different beings, as if we’re untouchable, as if nothing ever happens to us, but we’re people. Of course we’re privileged but in the tangibles we’re the same.”

The same? Or perhaps even worse off? Does the exposure, the pressure, the competition and need to perform, the public profile, make it harder? And few jobs expose people so young. The response is swift: “We’re not martyrs,” Iniesta says. “Lots of people would swap with us. Every job has its difficulties. Every time my dad, a builder, went up on the scaffolding, he could have fallen. But he accepts that risk; he had to. Or the lorry driver, or any job… the footballer knows; he grows up with pressure, criticism, having to be strong. I’m convinced there are many who wouldn’t make it.”

Iniesta left home to join Barcelona as a 12-year-old, crying alone in a corner daily. He says the worst night of his life was the first he spent at La Masia while his parents drove back to Fuentealbilla, Albacete in a Ford Orion that kept breaking down.

“We’re lucky to be footballers; my intention in explaining that bad moment is not to make people say ‘poor thing’, far from it. Just that elements of [a footballer’s] life, the feelings, the difficulties, are like anyone else’s. This is how people’s lives are. I don’t think I’m an exception. It costs una barbariedad – a colossal amount – to get to the first team and even more to stay there. I spent my whole life at Barcelona, living with the pressure from the age of 12. But you’re born a footballer, wanting to be one, so it doesn’t matter how old you are.”

For almost a year it was as if he was not one, his identity lost. South Africa brought him through and brought him here; Iniesta admits that it allowed him to “feel like a footballer again”.

Andrés Iniesta strikes the winning goal against Holland to secure a first ever World Cup title for Spain. Photograph: Matthew Ashton/Corbis via Getty Images

Some footballer: captain of Barcelona, universally admired, the man of whom Lionel Messi says that, when there is a problem on the pitch, the thing he wants most is to have Andrés close. Winner of over 30 titles; two trebles; every trophy there is; a European Cup winner in 2006 (although he admits that Frank Rijkaard’s handling of the final, which he began on the bench, “doesn’t sit well at all”), 2009, 2011 and 2015; a European champion in 2008 and 2012; World champion in 2010, scorer of that goal.

And he is not about to stop. At 32, no longer playing alongside Xavi Hernández and with Barcelona embarking on a stylistic shift, more direct, it might have been natural for Iniesta’s career to draw towards a close. He might have appeared the natural victim; instead he is enjoying this as never before. He became more central in every sense, a kind of Iniesta and Xavi.

The qualities that define him have not diminished; his game is, he says, “intuitive”. Recognisably his: summed up in that photo surrounded by opponents, bigger and more numerous than him. Almost as if it is deliberate, drawing them in, even if he protests: “I prefer one than five!” He explains: “I’ve never seen being small as a disadvantage; everyone has his qualities. Don’t ask me to beat a guy who’s 1.80m in the air: ask me to do other things I’m better than him at.

Andrés Iniesta finds himself outnumbered five to one against Italy at Euro 2012. Photograph: Markus Ulmer/Motivio/Cleva Media

“Most things come from inside, they’re intuitive; that’s the way I am. There’s tactics, strategy but I understand football as something unpredictable, because you have to decide in a thousandth of a second. If the ball is coming and there’s someone behind you, I’m not thinking: ‘I’m going left or should it be right?’ I just go and it comes off … well, sometimes it doesn’t.”

From across the room a friend is listening. “It always does,” he shouts, laughing. Iniesta squirms a bit and heads in another direction.

“Things have changed a bit but the essence will always be the same,” he says. “Everything evolves and changes need time: we didn’t play as well in September [2014] as in [the final] in the 2015 final in Berlin. The style is a product of the players; you have to use [Messi, Neymar, and Suárez] and maybe the midfielders have more pitch to cover, but I’m not someone who can only play a certain style or system. Last year was one of the seasons I most enjoyed. I broke my kilometre record, for sure, but that’s not incompatible with my style.”

The balance under Luis Enrique bears that out: a treble and a double. Now as they begin another season, a familiar face stands before them in the Champions League: one that looked out from posters by Iniesta’s bunk. The coach who changed the club and changed his career – and whose career Iniesta changed too. Barcelona versus Manchester City: it is not the draw they wanted but better now than a knock-out. And the reunion will be a fond one.

After two games under Guardiola in 2008 Barcelona had not won and the pressure was huge. Why they had chosen this novice over José Mourinho? One day there was a knock on Guardiola’s door. It was Iniesta. “Keep going, mister. We’re training bloody brilliantly,” he said.

“Things hadn’t started well but I believed in [Guardiola],” Iniesta says. “I felt a connection. When things come from inside, you know they’re real. I felt that way, like I had to tell him, support him.

“We came back from Euro 2008 and went to St Andrews and you could already see that this was different: the training, the communication, how the manager was. Until then there hadn’t been such a defined style and I identified with it. It changed everything and we needed that.

“Since then, if you watch, there are things other coaches have taken on that weren’t done until then: the central defenders coming out to play, or the full-backs. Pulling the pivot further back to begin [moves]. In sessions, instead of the two interiores coming back to receive, he pushed us further forward for the next wave, supporting players higher, offering passing options. You could only come so far; you can’t go past this line,” Iniesta says, signalling the limits with his hand. “And they’d watch to make sure, or there’d be cones marking out [that limit].

Pep Guardiola and Andrés Iniesta will be reunited when Barcelona face Manchester City in the Champions League. Photograph: Alvaro Barrientos/AP

“All those ideas were expressed early in sessions. Or, the pressure on the ball after losing possession… There’d be drills where, if the opposition plays six passes without you getting it off them, they get a point.” Or the goalkeeper? “Yes, he’s always been important for us, another player: when the ball comes out from deep, depending on whether your opponents have one or two [forwards], the goalkeeper plays. He allows you to have numerical superiority.”

The Artist: Being Iniesta is published by Headline on 8 September 2016.

Joe Hart has found that out already. But will Guardiola’s philosophy work in Manchester? “Pep knows how to adapt and I’m sure he’ll do so in England,” Iniesta says. “He’s also got staff like Mikel Arteta who’ll help that process, who know the league.

“City have signed well and have a very competitive squad. I know Nolito well because he was a team-mate here at Barcelona and with Spain. He’s had a great start and hopefully can continue. I’ve admired David Silva for years: I think he’s exceptional. Players learn day to day, from experience, team-mates and managers. I learnt a lot with Pep; he helped me to improve and he’ll do the same at City.”

Above all, though, Guardiola wanted Iniesta to be Iniesta, not least during those months when he was not. Because when Iniesta is himself, he is unique. Fuentealbilla with his friends is not the same as the Camp Nou with 98,000 fans – “If only,” he says – but while the stage marks you, the pressure too, some things remain. “What I do in the stadium, I did on the school playground,” Barcelona’s captain says. “What I did at 12, I still do now.”

• In the UK, the Samaritans can be contacted on 116 123. In the US, the National Suicide Prevention Hotline is 1-800-273-8255. In Australia, the crisis support service Lifeline is on 13 11 14. Hotlines in other countries can be found here

• The Artist: Being Iniesta by Andres Iniesta (Headline, £9.99). To order a copy for £8.19, go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min. p&p of £1.99.