The 23-year-old has two years left to run on his Breda contract but has become hot property since finishing as top scorer for winners Holland at the European Under-21 Championship.
Breda director of football Earnie Stewart told the Daily Mail: "We are in the process of negotiating a new improved contract with him but, if he wants to speak to Celtic, there is nothing we can do about it because it´s all been done by the book. Celtic have faxed us a note of interest and are the only club so far to do that."
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