Sunderland says it has completed the signing of Greece midfielder Charis Mavrias from Panathanaikos on a three-year contract for an undisclosed fee.

The 19-year-old Mavrias, who has played twice for Greece, made 70 appearances for the Greek club after coming through its youth academy, scoring six times. He made his debut at 16 in the Champions League in 2010.

Sunderland lost its first Premier League game of the season at home against Fulham and travels to Southampton for its next match on Saturday.