The 22-year-old joined United from Guadalajara last year and has become a success at Old Trafford.
Martinez admits the striker was to expensive for the Latics.
“He was a player that went out of our market,” Martinez said.
“But obviously he’s a real talent who Manchester United probably captured before he caught the eye of anyone.”
On the Mexico international’s performance against Wigan on Saturday, Martinez added: “He looked really, really sharp and very lively.
“He’s taken the step up into the Premier League really well and he has real quality.
“He is one of the most natural finishers in the league and he has only been here a few months.
“Everyone was aware of him when he played for Mexico. After the World Cup you could see he was ready for a big club. He is tactically impressive and a real asset.”
