Bayer Leverkusen star Hakan Calhanoglu will serve a four-month suspension, ruling him out for the rest of the season.
The Court of Arbitration for Sport (CAS) upheld a punishment handed down by FIFA, which found him guilty of breaching a contract with Trabzonspor, who he had agreed to sign for as a teenager.
Calhanoglu, 22, was also ordered to pay EUR100,000 compensation to Trabzonspor.
The offence relates to 2011, when the attacking midfielder agreed to sign for the Turkish side before opting instead to extend his contract with German club Karlsruher SC.
Leverkusen first revealed Calhanoglu was involved in a legal dispute with FIFA in March 2016, but he was allowed to play on while the charge was contested.
"The Court of Arbitration for Sport (CAS) has issued its decision in the dispute between the Turkish football player Hakan Calhanoglu and the Turkish football club Trabzonspor," a CAS statement read on Thursday.
"Hakan Calhanoglu is ordered to pay EUR 100,000 to Trabzonspor FC. Furthermore, the four-month ban imposed on Hakan Calhanoglu by the FIFA Dispute Resolution Chamber (FIFA DRC), which was suspended at the beginning of the CAS proceedings, is reinstated with immediate effect."
The ban will keep the Turkey international out for the rest of 2016-17.
Leverkusen remain in Champions League contention - they face Atletico Madrid in the last 16 later this month - and sit ninth in the Bundesliga, seven points adrift of the top four.
The club have reacted with fury at being deprived of one of their star players for an incident that took place long before they signed him from Hamburg in 2014.
"Of course, we regret this decision which is completely incomprehensible for us," said sporting director Rudi Voller.
"It's a heavy blow for Hakan but also for us. We are also being heavily punished, although Bayer Leverkusen had nothing to do with the events in 2011. We are now missing a very important player in a crucial phase of the season."
Michael Schade, Leverkusen's CEO, added: "In addition to the player, it also affects the club that played absolutely no part in the events of the time. Unfortunately we are left with no alternative but to accept the decision."