Sunderland midfielder Jan Kirchhoff is expected to be out for 12 weeks after having knee surgery.
The 26-year-old German tore cartilage in his knee during the Premier League defeat by Chelsea on 14 December, coming off after 57 minutes.
Kirchhoff was making only his eighth appearance of the season, and had two months out with a hamstring injury.
Sunderland, who visit Manchester United on Boxing Day, are 18th in the Premier League and one point from safety.
Black Cats forward Duncan Watmore is out for the season with a cruciate knee ligament injury.