The Court of Arbitration for Sport (CAS) issued its decision over the dispute between Calhanoglu and Turkish football club Trabzonspor on February 2.
In 2011, Hakan Calhanoglu was paid €100,000 ($108,000) after agreeing to sign for Trabzonspor in the future, when he was a youth player at German club Karlsruher.
In 2013, Trabzonspor lodged a claim to FIFA arguing that Calhanoglu had breached the terms of their employment contract without just cause when the player signed a contract for Karlsruhe.
The 22-year-old Turkish international had to pay €100,000 to Trabzonspor.
Calhanoglu's ban caused him to miss the final 16 matches of his team's Bundesliga campaign, also Leverkusen's UEFA Champions League last-16 tie against Atletico Madrid.
Germany's first football division Bundesliga welcomed the midfielder, with a headline 'Welcome back, Hakan Calhanoglu!' posted on its official webpage.