Martinez rates Stones among the best young English defensive talents running around today.
He told the Liverpool Echo: "In my eyes he's the most promising young English centre half that we have in the country.
"I expect big things from him but we need to allow him to develop and enjoy his football. He has a fantastic future ahead of him.
"It was frustrating to miss out on him in January, because I always thought he was ready to play in the top flight. As a player you need to make a decision and we had to accept that (at Wigan).
"So I was delighted when I got here to have him in the squad finally."
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