The Spaniard was criticised last season for a string of poor performances but has bounced back strongly this year with a solid campaign in the United goal.
Van der Sar told the Daily Star: "I think De Gea is progressing. He had a fairly hard first year but he is getting used to that pace and showing the ability that made Sir Alex Ferguson sign him.
"That is fantastic for the club and himself, of course. He makes a lot of saves with his feet – but so did I.
"He's a good keeper and I think the environment at the club really helps new players. Some players take longer to adapt but after just one day it felt like a warm bath when I came in."
De Gea has been part of the United defence that is the third best in the Premier League this season, conceding just 33 goals in 31 games.