Atalanta forward Ademola Lookman has handed the club a formal transfer request, he said on Sunday.
Lookman made the announcement with a statement posted on Instagram.
The 27-year-old said the request was made "after many months of broken promises and what I feel has been poor treatment towards me as both a human being and as a professional footballer.
"Sadly I feel I have no choice but to speak out for what I believe is right and I feel that enough is enough," he said.
He said in the statement that it had already been decided that it was the "right time" for him "to move on and experience a new adventure."
He said he and the club ownership had been "in agreement" that now was the right time for a transfer, and that the club agreed to let him leave if a fair offer was made.
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He said an offer did arrive but now the club was not sticking to its end of the agreement.
"Despite now receiving an offer in alignment to what I believe had been discussed, sadly the club are blocking the opportunity for reasons I do not understand," he said.
Lookman did not give other details about the offer.