Sunderland AFC defender Dennis Cirkin has undergone surgery on his left hamstring.
The 21-year-old, who last featured in November, is now expected to be out of action for a minimum of 12 weeks, as he starts a rehabilitation programme at the Academy of Light.
After suffering a significant knee injury during the festive period, Niall Huggins has also undergone surgery and the defender will miss at least the remainder of the campaign.
Forward Bradley Dack is continuing his recovery from a hamstring injury, with Patrick Roberts expected to return from a calf injury next month.