The Spain Under-21 international was voted the Premier League’s goalkeeper of the year in April after a string of impressive performances in the second half of the campaign.
De Gea made a series of high-profile errors in the early stages of his Red Devils career after sealing an £18m move to Old Trafford from Atlético Madrid in 2011.
Van der Sar, who was replaced by De Gea at Old Trafford, heaped praise on the 21-year-old for his noticeable improvement over the past 10 months.
“It is unbelievable,” said Van der Sar. “He came from different league, he was young. He was 20 when he came.
“He came from Spain, he didn’t speak the language. There is different food, different tactics, different methods of training.
“Corners and free-kicks, balls in the box – that is different to the Spanish league. It was normal he could have some troubles in the beginning.
“I think the way he turned the corner from January onwards has been a real benefit for United and one of the two or three reasons they won the league.
“His physique is better. He worked really well with (former goalkeeping coach) Eric Steele and the physical coaches and that is the way you improve.
“He is still so young but already experienced. Hopefully he will get a chance in the national team also.”
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