Van der Sar says De Gea will be under pressure to live up to his standards.
"Maybe it was hard to follow in my footsteps," said Van der Sar. "It can happen. People got compared to Peter Schmeichel, now maybe it's me.
"De Gea has to ignore that and just play his own game.
"Eric Steele, the goalkeeping coach, and the manager will both help him and hopefully next season he will be ready from the start."
"The main thing is how you recover in the next game, or the game itself. He did that. He became more important as the season went on and made good saves.
"I have not seen him in his shorts, so physically, it is difficult to say how big he actually is. But I am sure United knew all that when they signed him, so would have been aware of what to expect."