Sunderland have confirmed that winger Charis Mavrias has returned to Panathinaikos on loan until the end of the season.
The 20-year-old Greek has not made a senior appearance for the Black Cats during the current campaign.
Mavrias joined Sunderland from Panathinaikos in 2013 for a reported fee of £3m.
Sunderland are back in action on Tuesday when they travel to Fulham for an FA Cup fourth-round replay.