A press release posted by Bayer Leverkusen on their own website on Thursday confirmed that Calhanoglu, 22, was involved in a legal dispute with the Turkish club. It said the case involved a contract that Calhanoglu signed with Trabzonspor when he was just 17, and therefore not legally an adult.

"The agreement envisaged the midfielder playing for Trabzonspor from the 2012/2013 campaign," the statement said. "The move did not take place at the time primarily due to the lack of agreement between Hakan's former club Karlsruher SC and Trabzonspor."

The Mannheim native made his professional debut with Karlsruhe in the second half of the 2011-2012 season.

According to Leverkusen local newspaper "Express," Trabzonspor paid a total of 100,000 euros ($113,000) to Calhanoglu and his agent as part of the contract in 2011.

The Turkish newspaper "Sabah", meanwhile, reported that the contract included a clause that set out a one-million-euro penalty if Calhanoglu opted to sign for any professional team other than Trabzonspor. Bayer Leverkusen has not confirmed either of these stories.

The club's statement noted that although the case was not expected to be decided for several months, this would not affect his eligibility to play.

pfd/ (dpa, SID)