Hakan Calhanoglu will miss the rest of the season after FIFA's ban was upheld. Ina Fassbender/Anadolu Agency/Getty Images

Bayer Leverkusen midfielder Hakan Calhanoglu has said he will no longer allow his father interfere in his career after the Turkey international was hit with a four-month ban for breach of contract.

Calhanoglu, 22, must serve the ban after the Court of Arbitration for Sport upheld an earlier FIFA verdict, reinstating it with immediate effect. He must also pay €100,000 in compensation to Trabzonspor.

The ban was issued after an incident in 2011, when Calhanoglu, then playing for Karlsruhe, was paid €100,000 after agreeing to sign for Trabzonspor in the future. Despite the agreement, he subsequently extended his deal with Karlsruhe and the following year left for Hamburg, who loaned him back to KSC for one season.

"I was 17 and played at Karlsruhe," Calhangolu told Express. "A friend tipped me off that my father met with Trabzonspor representatives in a restaurant in Darmstadt.

"When my father returned, he told me: 'Hakan, you need to sign that contract.' In our culture, fathers have the last word, and it's out of place to not show them respect.

"I was 17, and not aware of the implications. I only had football on my mind."

The Turkey international said his father admitted he had made a "horrible mistake" but added: "He will no longer interfere in my career."

Leverkusen were not involved in in the breach of contract but will now have to resume their campaign without one of their key players.

Calhanoglu, a set-piece specialist who has scored six goals and provided five assists for Leverkusen this season, said he believed "this issue will only make me stronger" but it makes him "sad" to damage his club.

"I have feelings of guilt," he said. "I am so sorry."