The 2008–09 season was Olympiacos' 50th consecutive season in the Superleague Greece, but they are competing in the UEFA Cup after an 11-year participation in the UEFA Champions League, as they were eliminated in the UEFA Champions League third qualifying round by Anorthosis. In the beginning of the summertime, Olympiacos unveiled Spanish Ernesto Valverde as their new coach.

Note: Flags indicate national team as defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality.

In Note: Flags indicate national team as defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality.

Total spending: €23.8 million

Out Note: Flags indicate national team as defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality.

Total income: €5.5 million

Note: Flags indicate national team as defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality.