Bayer Leverkusen have said midfielder Hakan Calhanoglu is in a legal dispute with FIFA over a contract he signed with Turkish club Trabzonspor as a 17-year-old.
Calhanoglu came through the ranks at Karlsruher, for whom he played from 2009 until 2012 and on loan in the 2012-2013 season.
The Turkey international, now 22, signed the 2011 deal with Trabzonspor to play for them in 2012-13 -- but the move never went through.
He signed the contract with Trabzonspor "when he was 17 and thus still underage," Bayer Leverkusen said on their official website.
The statement added: "The contract said that he would play for Trabzonspor from the 2012-13 season on.
"However, the transfer never happened, first of all because his old club Karlsruher SC and Trabzonspor never agreed terms.
"The proceedings are expected to go on for several months. Hakan Calhanoglu remains eligible to play."
Calhanoglu joined Leverkusen from Hamburg in 2014.