AZ Alkmaar claim David Connolly signed a three-year contract with the club this summer and must play for them instead of Wimbledon.
The 24-year-old Republic of Ireland striker, who spent last season with Excelsior and Feyenoord, did not show up for training last Friday, and the Dutch side learned the following day he had signed for the Dons.
"We are not looking for any kind of claim," said AZ director Jan Kasper. "We just want Connolly to keep his part of the deal. What happened now is just impossible."
AZ have asked the Dutch Football Association to assist them and may seek a FIFA ban on the player if the matter is not resolved.
Connolly scored 13 goals for Excelsior in the Toto Divisie last season before netting five times for Feyenoord in the top flight.
PA