Martinez has held back the on-loan Barcelona winger so far this season.
He told evertonfc.com: "Every week he is getting stronger. I thought his impact in the first half at Fulham and in the last 15 minutes was quite impressive. He is the sort of player that can win you games. He was electric and looked strong physically.
"He is still learning the differences of the two leagues and that is understandable - it is going to take time and we need to give him that time - but I am very pleased with his attitude and the way he takes opportunities every time he is on the pitch.
"I will need to keep thinking about when to allow him to be on the pitch but I'm very excited by his talent and his potential to win games for Everton."
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