The midfielder looks a natural at Premier League level and is already capped by England.
Martinez said: "Ross can be as big as he wants. I think when you get a player that's got the talent and the ability that he has, I see it as a unique talent for the English game, not just Everton.
"I've been immensely impressed, but not surprised by him because when you see someone with that talent, you know straight away that it's someone special.
"I think he will be a big player for England, too.
"That's down to the England manager, but he's one of those players that any manager would want in his team."
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