The Spaniard was in fine form as the Red Devils earned a 1-1 draw at the Santiago Bernabeu in the first leg of their Champions League last-16 clash with Real Madrid on Wednesday.
And Chicharito, who was an unused substitute for the game in the Spanish capital, has backed the 22-year-old to continue improving.
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"A lot of people who know about football know that David is a top-class goalkeeper," he told MUTV.
"That is why Manchester United bought him. They saw how good he can be. If he wasn't at the right level to play at this club he wouldn't be here and they are trying to look after him.
"To me, he is a complete goalkeeper. You see the great saves he made on Wednesday. He can also play with his feet, which is very useful to see in a goalkeeper.
"Other people are speaking about when he has to go out and clear the corners and free-kicks. They say that is the weak part of his game.
"But I think he is doing brilliant and in a couple of years he will be the number one in the world."
De Gea had previously come in for criticism after some high-profile mistakes early in his career at United, but Chicharito says the Madrid-born shot-stopper is unconcerned by such talk.
"David is very focussed and doesn't care about what people say about him," he continued.
"He has a lot of confidence. He doesn't need to listen to what people say about him. He should just play and enjoys it because he knows he can be number one in the world."