On 2 July 2017, AEK Athens and Empoli have reached an agreement for the transfer move of the Serbian central defender to the Superleague Greece club. The 25-year-old former player of Red Star Belgrade, Pescara and Frosinone, who made 14 performances during 2016–17 season at Serie A with the struggling Italian team, is expected in Athens in order to complete the final details of deal and sign his four-season contract with AEK. On 3 July 2017, after successfully passing his medicals he put pen to paper to a three (plus one) years' contract. AEK paid €500,000 to acquire Ćosić from Empoli, which has a resale rate of 25%.