De Gea has been under intense scrutiny this season and continues to make mistakes despite being widely thought of as one of the best shot stoppers in the Premier League.
The Spanish ‘keeper was awarded Man of the Match in United’s plucky draw at Real Madrid on Wednesday night in the Champions League last 16 first leg.
Many pundits have criticised De Gea in recent weeks as he looks nervous when coming for crosses and his distribution is far from ideal.
United have been linked with making a summer move for Stoke City’s Asmir Begovic with De Gea linked with a return to Spain with Barcelona.
Hernandez has been impressed with the 22 year old this season and is adamant that he will become the best goalkeeper in the world in the coming years.
“A lot of people who know about football know that David is a top-class goalkeeper,” the Mexican striker 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.”