The midfielder was named to England's World Cup qualifying squad yesterday.
Martinez said: "Ross is as good with his left foot as he is with his right. When he broke his leg, it took him three months to get back to his normal self and he started using his left foot. Now you won't see a difference between which foot he strikes the ball with.
"He's started our last three games. Against Real Betis (in pre-season) he gave the ball away twice in a dangerous area; against Norwich it was once and against West Brom, he didn't. It's incredible how he takes things in and can develop - but he's not the finished article.
"I have spoken a few times (with Roy Hodgson), but England know him well. They have always had high hopes for him. When England won the (UEFA Under 17) tournament, Ross was the main player. But then he broke his leg."
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