But he insisted: "Javier is one of the most exciting young prospects we've seen at the club for some time.
"You obviously have talent when you come to this club but his work-rate and his attitude are phenomenal.
"He's tough, he has grown up in Mexico. But what sets him apart for me is his work-rate every single day.
"He has the right attributes to go with his talent.
"He works so hard and has done so well since he came to us. You get rewards for that. He will score lots and lots of goals for this club."