The 22-year-old, who came under criticism in the early stages of his career at Old Trafford, received plenty of plaudits for his form during United's Premier League-winning 2012-13 campaign.
"For me, he's the best goalkeeper in the world," Sky Sports News quotes Hernandez as saying. "Last season he really benefited from being given the opportunity to play on a regular basis.
"He was first choice and any player in the world shows his true ability when he gets the chance to have a decent run of games in the side. David has really shown his quality. He's doing very nicely, thank you."
De Gea was also part of the Spain Under-21 team that clinched the European Championship trophy in Israel this summer.