De Gea endured a difficult start to his career in England, with question marks raised to his reliability and ability to adapt to the physicality of life in the Premier League shortly after completing a move from Atletico Madrid in 2011.
The 22-year-old has shrugged off the criticism, though, and worked hard on improving his game.
His efforts were rewarded in 2012/13 as he played a prominent role in United's title success, earned a place in the Premier League team of the year and helped Spain to defend their European U21 Championship crown.
Hernandez is delighted to see De Gea getting the recognition he deserves, with it his opinion that the Red Devils now boast the most complete shot-stopper in the global game within their ranks.
The Mexican striker said: "For me, he's the best goalkeeper in the world.
"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."