There was something wrong with the way Marc-Andre ter Stegen ran, which was lucky. Had there not been, none of this might have happened. He might have given up right then and there, 15 years ago, and you might never have heard of him. He was 10 and playing for Borussia Monchengladbach, where he'd been since the age of 4, when his coach broke the bad news. He was only a kid but there was something in his style that wasn't quite right and maybe never would be either; enough to end it, anyway. "Strange," the coach called it.

Is there still?

"I don't know," says Ter Stegen. "Other people need to judge that."

So let's judge. He might need to speed up to show it but if there is, you can't see it in the way he walks. Not from here as he strolls around Barcelona's San Joan Despi training ground, heading for the artificial turf pitch with a football in his hands, and there's nothing wrong with how he kicks it either. When he gets there, he places it on the penalty spot and, wearing jeans and trainers instead of boots and kit, clips it towards the crossbar. He hits it, too. Admittedly not at the first attempt, which misses by a centimetre or two, but by the third, which is pretty good.

Well, it is what he does. Apart from all the saves and stuff. It is what he did, too.

"I started as an outfield player," he says. "I started playing as a striker. At the beginning, it is all about fun. I had a lot of fun. But then when I was 10 years old, more or less, I had a coach who said that I had a strange running style. I was about to leave... I had a decision to take: if I leave or if I stay, but as a goalkeeper. Sometimes I was playing in goal and he was very happy with that. And I was OK, I was confident in goal, I played there in my free time a bit, in small games and stuff, so that was OK."

OK? It turned out a bit better than OK. The ball pings back off the bar.

One of the things that most stands out about Ter Stegen, maybe even the thing that is commented upon most, is that he is a goalkeeper who is good with his feet. He's often seen clipping perfect passes to teammates and stopping a thousand hearts as he avoids tackles from opponents, dribbling around them like there's ice in his veins; a goalkeeper who, in his own words, is "trying to play, one more [outfield] player when we have the ball, trying to give my colleagues options, keep the match moving, helping them find good solutions."

Just how good is he, then? All right, no one is expecting him to be better than Lionel Messi but might he not be the worst player in training?

There's a long pause. Bloody hell, he's thinking about this. Might he actually be better than some of them, even at a team like Barcelona? Eventually he laughs and finds an escape, like one of those drag-backs of his taking him past an on-rushing striker. "I'm concentrated on my hands," he replies, a glint in his eye.

Well played, sir.

And, ah yes, your hands. Everyone rated him highly anyway, but maybe all that talk about his feet has tended to disguise how good Ter Stegen is at the things goalkeepers are supposed to do. Until recently, at least: this season, the eulogies have become unanimous. He has spent a good part of the campaign saving his team, after all. Try this for a stat: as Barcelona headed into November, they had faced 24 shots. He had saved 23 of them. And you can bet he watched that one more than the other 23.

In his fourth season at Barcelona, Marc-Andre ter Stegen has become one of the best goalkeepers in the world. fotopress/Getty Images

Now, it is legitimate to ask whether he might be the best goalkeeper in the world. Just don't expect an answer from him on it. And it is not false humility, exactly. It's something simpler than that; it is that he has no one really to compare himself to. Thoughtful, analytical and determined, Ter Stegen talks about his trade but not its tradesmen.

In more than an hour with him, only Manuel Neuer, his international teammate, gets anything more than a passing mention when he dismisses the suggestion that German fans might be thinking there's no need to rush their goalkeeper back for the World Cup now that Ter Stegen is around.

"No. For sure, not," he says. "When he comes back, he is the No. 1, he deserves a lot of respect and I think all of us are trying to help him to be at his best because in the end it is a team situation, we want to be successful as Germany, so we always try to push our team members."

Oh, and Claudio Bravo of course, because he once stood in Ter Stegen's way. So that's more about him really. And that is pretty much that. Even Thibaut Courtois, his opposite number next week, doesn't exercise his mind much. Chelsea's forwards, on the other hand, are a different matter.

"I don't watch goalkeepers to be honest," he says. "I got asked if I am following Courtois. I said 'I'm not watching too much Premier League and I'm not really focused on other goalkeepers.' I watch highlights, which is the minimum I can do, but as we are playing every three or four days the focus has to be on what we do, on myself.

"And I don't need to decide [whether I am the best in the world]. I just try to be there, to be 100 percent, to be concentrated, and to show every time that I can perform -- for the team. It's only about the team, nothing more. I mean, if I am playing well, others will feel confident, they will feel fine, and that's what I can do."

"Confident" is the word. "Concentration," too. There is something unshakable about Ter Stegen, unusually so. He's still only 25, don't forget. Yet it's like he has no doubts -- none that he wants to show, certainly -- and there's a conviction in everything he says, in perfect English and impressive Spanish, too.

He doesn't watch goalkeepers -- he is not competing with them -- but he does watch strikers. He talks about the videos and reports, about the preparation, although he says that sometimes you can be too prepared, too pre-conditioned by that study. He talks about watching a player's movements and body shape, the way he places his foot, small details "you wouldn't even imagine" -- the intuition born of years of doing this.

As he does so there is a sense of control. "Balance," is the word he uses. Like a man who knows where he is, every detail of his profession, but without being drowned by it. Or almost every detail. And if he doesn't know, he wants to.

So how tall is the goalpost?

There is a pause as he thinks about it. "Two... thirty-eight, or something..." he suggests.

It is not such a silly question. Well, it is. But there's a reason for it. Victor Valdes once said that ...

"Woah," he interrupts. "Well, was that right first of all ...?"

Ah. Erm. Actually, it's 2.44 metres (eight feet) but honestly, that needed looking up later. The point, though, is that Valdes once said that at Barcelona, the goalpost doesn't measure what it measures elsewhere, such is the pressure. It is different too; the way Barcelona play, he said, means that the degree of focus and concentration is so intense that you can only touch the ball once but still end the game exhausted, "in pieces." That sometimes you just want to get away from it all. Valdes liked windsurfing, he said, because out there, there is no one to bother you; just the occasional fish swimming past.

"The measurements are the same but of course I know what he means," Ter Stegen says. "I feel good, I am happy here, I feel that it is normal. It's three and a half years now and the pressure is bigger of course but that's what it's like at a big club. I am not feeling too much pressure from outside as I am always trying to be focused on what I am doing; that's how I treat it.

"But it is true that the concentration is super difficult. Sometimes you have faced no shots during 90 minutes and in minute 91 there is a shot. You always need to be focused, concentrated, and this is what makes you tired, being so focused. He is totally right. I try to be concentrated. Sometimes I talk to myself, but it happens just a few times. I try to say to myself that I need to be focused. Maybe they have one shot, or not even a shot, and you need to be there and you need to save that ball.

"But you always have chances [to be occupied]: you play with your feet, you're passing, you always have situations in the game. What I think is very important is always to be focused. You need to be 100 percent no matter what. It is difficult, but you need that. There is no chance to relax."

There is, though, time to think, and that may not always be a good thing. Standing there alone, mistakes can eat away at your mind. Maybe there's a facade, yet even those moments don't appear to faze him. The criticism must sting sometimes, but if so it doesn't show.

"Of course, it's not nice sometimes, but this is our profession, our job, and we always try to be happy, confident. It can be difficult: if you fail one time you will see it in every highlights [reel]. But this makes it so interesting ..."

Almost part of the thrill?

"Exactly. I love my profession. I am human and of course I can make mistakes, even if nobody allows them."

Some glory in them. Fans try to remind you of them, putting you off. And no player is a target like a goalkeeper is, alone and exposed, close to the stand. "I love that comments of the fans, I love when they try to make you insecure and if they are all whistling, it's the best ...," he says. "I'm just smiling because it's so nice; it would be strange if they didn't whistle when you went out. Fans try to make you insecure. In the end, it doesn't matter how you do it, but you need to perform.

"I am trying to learn about my mistakes. You can't change that moment. Mistakes will always happen and to minimise these is the most important [thing]. When you made a mistake, it is done, you can't change it any more. you need to look for the next ball. I am always trying to be concentrated, not to think about too much of what has passed. I'm never thinking: 'Oh, s---, you made a really bad pass ... you could have done better.' Because when you think about the last situation, you will fail in the next one as well.

"I trust my teammates, 100 percent, and they do the same to me. I try to give back and when you give back they are happy with it. I'm always relaxed, and I try to be focused on the next situation."

Ter Stegen has played all 23 of Barcelona's league games this season, conceding just 11 goals. AP Photo/Thanassis Stavrakis

More, always more. And so here he is. Secure, unmoveable, unquestioned. It wasn't always going to be this way. And there's something of the single-mindedness that really comes through in the directness -- the bluntness, even -- with which he deals with the moment that things might have been different. It comes up naturally, too. And it starts at the start. He wasn't always happy, he admits.

"Ivan Rakitic speaks German, so when we both came, it was very easy. I was asking him what they are saying, because I didn't know the language. He helped me a lot. He helped me in the team with the conversations and stuff and that made me calm," Ter Stegen says.

He grins. "I knew exactly what they were saying about me, which is also important.

"I feel like I'm home now: it's three-and-a-half, four years now. I feel good, my wife is happy, we both are trying to adapt as fast as possible to the mentality. This is why I wanted to speak the language as soon as possible. I am happy it has gone like this. At the beginning I wasn't that happy but now with one and a half years that I am the clear first goalkeeper it is a lot different."

And there it is.

The key. Another turning point, like the day his coach told him there was something wrong with the way he ran. That moment when his belief in himself was reinforced by the club's belief in him. It was decision time, and Ter Stegen won. "That showed me how much value I have for the club," he says. After two years of sharing goalkeeping duties, a situation that satisfied no one, something had to change.

Bravo departed for Manchester City and Ter Stegen stayed in Catalonia. It seems obvious now; it wasn't quite so clear-cut then. Things haven't gone well for Bravo since, they have for him.

"This is how football works sometimes," he says. "When he was here he was a very, very good goalkeeper who has a lot of quality and it was always a special relationship between us..."

But it must have been difficult: two goalkeepers who wanted the same thing and knew that only one of them could have it.

"Yes, it is. It is. Because at the end there is one point where the club needs to decide. Claudio also had a lot of value and he had the same intentions that I had: we wanted to play 100 percent, both of us, and not just, like, one plays Copa and Champions League, the other the league. I always wanted to go for 100 percent and he did the same, and in the end the club had to decide because it was a super-difficult situation, not just for the club but also for us.

"In the end, Claudio decided to leave. I'm convinced that he is still doing very good, that he is trying to give 100 percent. Even though he is not playing at the moment, not as much as he wanted to play, he made a decision which is important for life. Hopefully, maybe one time he will come back to Spain, you never know. We'll see how everything goes. But at that moment it was either him or me. And they decided for me."