“Doc, just take it out. I’ve got another one.” Saúl Ñíguez had made up his mind. He had had enough. He had spent months in pain and discomfort, urinating blood, his kidney was not working properly, there was no end in sight, no guarantees, and all he wanted to do was all he had ever wanted to do: play football. If that meant removing a kidney, then that is what he was going to do. Nothing else mattered. Until one day Atlético Madrid’s assistant coach Germán El Mono Burgos – a former goalkeeper, a rock singer and a great, big beloved bear of a man – looked him in the eye and offered his advice. “And then I saw,” Saúl says.

Listening made sense: Burgos spoke from experience. When he was diagnosed with cancer one Thursday in 2003, he asked doctors to wait until the Monday to remove the tumour as Atlético had a game that Sunday, but they insisted on operating immediately. Twelve years on, a clash with Bayer Leverkusen’s Kyriakos Papadopoulos on his Champions League debut in February 2015 resulted in Saúl being rushed to hospital, where Atlético’s president described his kidney as “destroyed”. “The worst thing,” Saúl recalls, “was lying on the stretcher and seeing my dad cry. I said: ‘Dad, it’s OK; I’m a toro, a bull, I can take this.’” Yet there were tough times ahead.

Saúl returned, playing with an internal catheter, yet the pain persisted and when the catheter was removed he was not fully cured. Doctors wanted him to stop, ease off, which was the last thing he wanted. “The catheter gives you functionality but it was sore, you’d feel it running, and I was urinating blood. Maybe some would say: ‘That’s it,’ but no [not me],” he recalls. “The problem was when we took it out, my kidney didn’t work properly. I was given options: play for a month, stop for a month ... I said: ‘No, no, that’s no good. Put the catheter back in, I can function.’ But they said: ‘Saúl, it’s not that simple.’

“I was tired of it all and I said: ‘Doc, just take the kidney out. Take it out. I’ll be out for a month, but then I’ll be back again. The doctor was saying: ‘I’m not taking your kidney out;’ ‘Try this;’ ‘Try that.’ I said: ‘Yeah, I’ll try things but if they don’t work, then what? More of the same? No. I just want to get back to playing well, feeling well. Forget it all. Be normal. Play football. I can’t be worrying about getting a knock. I just want to play. Take it out.’

“Mono Burgos was so important. He came to me: ‘The doctor says you’re talking about taking out your kidney. You’re 22! What are you talking about? Use your head.’ I was just thinking about football: take this out and play. I thought: lose a kidney, it’s fine, I’ve got another one. But Mono told me what he went through, he looked me in the eye: ‘Saúl, think about your life.’ I saw. The seriousness, the future. What if you get a problem with the other one? There’s no way out. And we put the catheter back in.”

It has been removed now, although Saúl says with a laugh: “I actually played very well with it.” Sitting at Atlético’s Cerro de Espino training ground, he looks well, but then for all the blood and discomfort, on the surface he looked well then too. And he is right: he did play well – almost as well as he is now. Diego Simeone says: “Saúl has all the qualities to be one of the world’s best midfielders: work-rate, touch, good in the air, passing, pace, rhythm.”

Attitude, too. “‘What doesn’t kill you makes you stronger’? In my case, I suppose it’s not just a cliche,” he says, but he has always been determined, tough, and you can hear it in every story, every word, rattled off fast. There is an assuredness about him, a directness and conviction. An awareness, too: football is not always nice, he has long known. He learned that himself – he joined Real Madrid at 11 but left a year later, the victim of bullying by team-mates who stole his clothes and set out to get him in trouble with the coaches – and through his family. “It’s in my make-up to never get sunk, but they ‘prepared’ me well,” he says.

Saúl’s father, José Antonio, played for Elche and his older brothers are footballers, too: Jonathan, 32, plays for UCAM Murcia in Spain’s third tier, 28-year-old Aaron is at second division Real Oviedo. They have always advised him, he says, and he is grateful, although the decisions are his alone. “For example, my dad didn’t want me to go on loan to Rayo Vallecano [at 19 in 2013]. My brother had loans that hadn’t worked and he worried. ‘You won’t return to Atlético, it’ll go wrong,’ uff. But I made the decision. I wasn’t afraid of anything.

“Aaron’s five years older and, thinking about it, maybe that’s part of it. At four I’d play with nine-year-olds, fighting, competing. They’ve kept my feet on the ground, given me incredible maturity. I left home aged 11 and I knew it would be tough, I knew I’d go hungry, I’d lose clothes. I knew what was coming. It was harder for them because they were the first to go; it wasn’t as hard for me because they’d seen it before.

“Aaron went from being one of the best, Spain’s No10 with the under-21s and under-19s, to disappearing from the map. He tore knee ligaments. His career had been all roses: he was with Valencia, Barcelona wanted him, Chelsea were interested, everyone was. Everything was wonderful, then suddenly nobody wanted him, they looked at him differently. He disappeared. After the injury, I’d say: ‘Bloody hell, Aaron, you have to get back to your best.’ He’d say: ‘Saúl, I’m grateful I can even run, jog, do a rondo, anything.’ I pushed: ‘You can give more’. ‘I can, but this takes time’. It becomes mental more than physical. A lot is in your mind.”

The demands Saúl made of Aaron, his father made of him. “I know how sad he gets when I have a setback, how it affects him. When I play a bad game I’m not the only one beating himself up over it; he does, too. He’ll say things like: ‘Saúl, that shot! If you want to be the best, you have to turn your foot inside’. That’s helped me set the bar very high. I want to be the best midfielder in the world. I know maybe I won’t get there but by aiming that high, saying ‘I want to be the best’, I’ll reach my best. And then I’ll be satisfied.”

The talent is there; so, too, the temperament. “I want challenges that really test me, very difficult ones. I was the same as a kid: when you play with players your own age it doesn’t bring out your best. At Atlético I always played with older players, sometimes out of position. I’d keep going back until I beat them. Hard things make me happy. You get upset but you mature and improve: the quicker you reach your best level, the longer you stay there. They say players peak at 28; I wanted to be there at 22, 23.”

Saúl made his senior debut at 17 years 108 days and it could have come sooner. “From very young, English clubs were interested,” he says. “Fulham wanted me when I was 15, playing in Atlético’s youth team, not always in my position. Mark Hughes was manager and I was close. It was a chance to play in the Premier League at 16. The plan was train for three months, then play. I was prepared to make that leap, ready, but things happened the way they happened and now I’m glad I stayed. Although it maybe took longer, I’m where I am today.”

Manchester United were regular spectators when he was at Rayo, there were huge offers this summer and more will surely follow but he insists he is in no hurry to depart and why would he be? After Rayo, Simeone wanted him to go on loan again but Saúl convinced him otherwise. At 22, he has played one Champions League final and aspires to another. He recently signed a new deal which Simeone considered vital. Atlético are unbeaten, entering a new era in a new 68,000-capacity home, a future to chase. From January they’ll also have Diego Costa – a £57m buy from Wednesday’s opponents, Chelsea.

“He’s very hungry. He’s a winner and that gene is important,” Saúl says. “He’s loco, a happy person, he has a vitality that’s good for the group. He transmits positive energy and never gives up. There’s a long ball, you think it’s a lost cause and then suddenly he appears and he’s fighting for it. If I see him chasing for everything, I feel obliged to chase too. That runs through the whole team. It would be incredible to win the Champions League and even better to do it this season, or next when we have the final at the Wanda Metropolitano. We know how difficult it is to reach a final, let alone win it, but it would be beautiful.

“If you sign until 2026 it’s because you mean it. It’s not as if I’ve reached a level where I can’t get better here. I want to give everything, to be the best. The club is growing and there’s still room to improve. It’s everyone here at Atletico, people who deserve all the gold in the world. It’s not just the people the public sees, it’s all those beneath the surface. They love this club, you can feel it. It’s like a family. And I have my parents, my brothers, friends, a partner who gives me tremendous stability. I have everything in life now.”

Saúl has health, a future and people who care. Such as Mono Burgos, who persuaded him to keep the kidney that bled in the BayArena, and José Antonio, who cried as he was carried to the ambulance. “Seeing my dad from the stretcher will stay with me for ever and I know have to give everything for him too,” Saúl says.