Javier Hernandez left Manchester United to join Bayer Leverkusen

David de Gea admits he was surprised manager Louis van Gaal allowed Javier Hernandez to leave Manchester United - and says the forward would be a certain starter if he was the boss.

Hernandez joined United from Mexican side Guadalajara in the summer of 2010 and scored 20 goals during his debut season at Old Trafford, helping Sir Alex Ferguson's team win the Premier League title.

But following Ferguson's retirement in 2013, the 27-year-old saw his first-team involvement reduced.

He featured sporadically during David Moyes' short reign in charge of United and was then sent on a season-long loan to Real Madrid following Van Gaal's arrival at the club last summer.

Hernandez returned to United in the summer and featured three times in August before being sold to Bayer Leverkusen, a decision which still perplexes De Gea.

When asked why he felt Van Gaal sold the Mexico international, De Gea told ESPN: "I don't know.

De Gea feels Hernandez would still be an asset for United

"These are decisions for the coach. But in my team, he would always play. He was an undisputed starter before and player of the year at United.

"He can get you 20, 30 goals a season. I would like a lot to play with him again, hopefully it can happen."

Hernandez has scored 10 goals since arriving at the BayArena and De Gea feels his former United team-mate is beginning to rediscover his best form.

"It is difficult for him, for any player, to play little," he added.

"They were difficult moments, but everyone trusts in him, knows the level he has.

"He always does something, always scores goals when he gets playing time. He is showing now he is among best goal scorers in the world."