Bayer Leverkusen midfielder Hakan Calhanoglu will miss the rest of the season after a four-month ban from FIFA was upheld by the Court of Arbitration for Sport (CAS).
The 22-year-old had been locked in a contract dispute with Turkish club Trabzonspor dating back to 2011, when the player - then a minor - reached an agreement to join the club, only to extend his contract at Karlsruhe and later sign for Hamburger SV.
FIFA ruled in favour of the Turkish club and imposed the ban, which was suspended pending the appeal.
"We regret this decision which we cannot comprehend," said Leverkusen sports director Rudi Voller. "Leverkusen is not involved in the dispute with Calhanoglu having joined in 2014 from Hamburger SV.
"This is a big blow both for Hakan and for us. Although Bayer Leverkusen had nothing to do with this it is also punished. Now we will miss an important player during a key part of the season."
Calhanoglu will also be suspended for Turkey's World Cup qualifying match at home against Finland on March 24.