Barkley was on the scoresheet in their victory over Newcastle United last night.
Martinez said: "Ross is a diamond of English football, but he still has a long way to go.
"Barkley is the sort of player who controls things in midfield, and that is unusual in a player his age. I think he is an exceptional ambassador, not only for Everton but English football as a whole.
"It is almost a question of keeping him away from the training ground because he is so eager to improve himself."
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