Roy Keane has confirmed that defender Russell Anderson will be out for three months after undergoing surgery on his ruptured ankle ligaments.
The 28-year-old Scot signed for the Black Cats in the summer from Aberdeen and had played two games for Keane's side before getting injured against Luton last month.
"Russell has had an operation and will be out for a while," Keane confirmed on Sunderland's official website.
It is one of a number of long-term injuries in his squad, with Kieran Richardson and Stanislav Varga both at least two months away from fitness.
They are also without Dean Whitehead (knee), Andy Cole (calf) and Carlos Edwards (hamstring) for their next few games, as the trio try to recover from spells on the sidelines.