Sunderland midfielder Lee Cattermole faces four months on the sidelines after undergoing surgery to address a long-standing hip problem.
The 28-year-old, who made the last of his three appearances this season against Crystal Palace on September 24, underwent a procedure to repair a torn cartilage last Monday.
Speaking at his press conference ahead of Saturday's home game with fellow strugglers Hull City, manager David Moyes said: "Lee had an operation in America. He is still out there just now but will be coming back in the next day or two.
"It's a big blow because we have had hernias, we have had epidurals, we have had other things done but, by all accounts, we have found a tear in his cartilage in his hip which has now been repaired."
Cattermole, who joined Sunderland in a £6m move from Wigan in 2009, has been a key figure in the club's successful battles to preserve their Premier League status over the last four years.