Mata's sale to Manchester United has disappointed Blues fans.
But Leboeuf told the Sunday Express: "I've never been a big fan of Juan Mata. I think he's a fantastic player (but) I think he doesn't suit English football.
"I guess Chelsea tried to find the new (Gianfranco) Zola. But Zola was much more powerful than Mata, and Mata is a little bit light.
"I think Mourinho realised that and that is why he bought Willian, because he has a little bit of Zola, not as big as Zola but strong, skilful and works really hard for the team and can defend."
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