I can only remember Sir Alex Ferguson missing two United matches. He missed a Manchester derby in 2000 for his son’s wedding. The other time? To scout the brilliant David de Gea.

I joined United in 2008 and, from that moment, we needed to be ready for the day Edwin Van Der Sar retired.

I was convinced that a 19-year-old De Gea was the right man to replace him. I showed a three-minute DVD compilation to Sir Alex and then we went to watch him play for Atletico Madrid at Valencia on the night United played Scunthorpe in the League Cup.

David de Gea celebrates after his team's victory over Arsenal on Saturday evening

The Spaniard made 14 saves as he team picked up a crucial three points in north London

Sir Alex knew he was the right signing inside 65 minutes. David showed composure, concentration and reflexes. He made one terrific save that went through a load of bodies.

It was a brave decision to commit £17m to a 19-year-old goalkeeper. Sir Alex had been patient with young outfield players before but this was the first time he did it for a goalkeeper.

People targeted David physically but we never changed our programme to improve him. We knew the strength and power would come. Sir Alex and I encouraged him the whole time. Sir Alex did not criticise him. Not once. He left him out at some stages and put him back in but he never shouted at him or put him down.

De Gea saves Alexis Sanchez's close range effort as Arsenal tried to mount a comeback

And just look at David now! His outstanding quality has always been his calmness and on Saturday night, amid all the penalty-box mayhem, he was a beacon of tranquility. He is the calmest man on the field.

He makes every kind of save, he dominates his penalty area. He is now the greatest goalkeeper in the world. Only Thibaut Courtois gets close at the moment in England but David is the best.

He deserves to be mentioned in the same breath as Peter Schmeichel. Think about it: Peter joined United at the age of 27, Edwin joined at 35. David, at 27, is only just entering his peak years. Believe me, he is only going to get better.

Tony Coton on De Gea

If it had been any other goalkeeper, we would have said his performance at Arsenal was surprising. But it wasn’t - and that is why I would argue that David de Dea is the best goalkeeper in the world.

For sheer consistency of performance at the level he has reached, I really don’t see anyone close to him. I don’t see any weakness.

It’s impossible to compare him and Peter Schmeichel, the Manchester United goalkeeper I worked with at the club in the early years of my decade as goalkeeping coach. They have completely different styles. Peter was loud, outgoing with a big frame. I would say he was slightly quicker than David.

The 27-year-old made more saves than any keeper has in a single game this season

But what David brings is the calmness, composure and – an aspect not always appreciated – an ability to get every angle right. He is a goalkeeper who has always done his maths. He always knows the geography of his goalmouth. From a professional perspective, that’s the part of his consistency that excites me most.

If people ever questioned him it was because of the physical side of his game but as a goalkeeper you don’t need to be physical or a cross-taker in the way you used to. Crossers of the ball put shape on it now and crosses are quick and low, so the keeper can’t come for it. It’s not like people are ‘putting it in the mixer’ much, leaving the keeper to be brave and claim it.

What shouldn’t be overlooked about David is the fact that he has performed during some difficult United years. When the goalkeeper is your Player of the Year, it says something about the size of his job through the season. David has won that prize in three of the last four years.

Tony Coton was Manchester United goalkeeping coach from 1997-2007. He was in conversation with Ian Herbert

De Gea's display further established him as as one of the very best goalkeepers in the world

Mark Schwarzer on De Gea

He is definitely up there and I have said this a lot in the last 12 months because he has been so consistently good.

He could still develop his all-round game because on his line he is probably the best goalkeeper there is. He just needs to dominate his 18-yard box more.

If he came out and took a few more crosses, and perhaps played a higher line and used his feet a bit more, he would be putting pressure on Manuel Neuer in terms of being the best in the world.

Neuer has the all-round game – he plays a higher line, dominates his 18-yard box, is exceptional with his feet and is very good on his line.

But look at those De Gea saves at the weekend. He is a big reason why Manchester United came away with the points.

Tony Coton’s autobiography, ‘There to be Shot At’, de Coubertin Books, is out now