The 20-year-old Belgian striker made a huge impact on loan with West Brom last season and Everton gratefully signed him in the transfer deadline scramble.
Former Manchester United, Aston Villa and West Brom boss Atkinson said: "A lot of questions have been asked about Chelsea up front, yet they release a young striker who looks a real talent. I'm very surprised at that decision.
"He was terrific for Albion last season. He is a real handful and he scores goals. And he can only get better in the months ahead."
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