Van der Sar believes De Gea is worth persevering with, however, despite acknowledging that he must learn how to deal with high balls into the penalty area.
He told the Telegraph: “I’ve been to the training ground a couple of times and have seen them both in action.
“David came in as a big talent. He started at an early age at Atletico Madrid, was given a chance because of injuries and showed himself to be a big prospect. That’s why United bought him. They saw him as the long-term replacement for me.
“David has great qualities, but I think at the moment, the high balls are his main focus.
“I know [goalkeeper coach] Eric Steele well, I spoke to him last week, and I know the whole team are working on every player to improve each one of them.”