Vela knows Hernandez well and will come up against his compatriot when Real Sociedad take on Manchester United in the UEFA Champions League on Tuesday.
He is convinced that Hernandez has the ability to flourish at Old Trafford but reckons he may think about leaving if he continues to find himself down the pecking order.
"Javier is my good friend - and I hope he gets lots of chances this season at Manchester United," Vela, who spent seven years at Arsenal without ever establishing himself, told The People.
"He is one of the best finishers in England and deserves chances under the new coach.
"If he plays regularly he will score, so I don't totally understand why a player of his quality has not played more games.
"If he doesn't play regularly he will need to think about leaving.
"You always want to succeed at the biggest clubs - but if he is not given the chance there will be big teams in England and Europe wanting him."
Sociedad are bottom of Champions League Group A after losing their first three games and Vela knows they have little chance of progressing in the competition, but he would love to claim the scalp of United.
He said: "We owe it to our fans to get a good result at home, and to beat Manchester United would be for them as much as for us.
"We understand it is nearly impossible for us to progress, but beating a team like United can really get our season going."