Elliott was forced into the option of surgery

Elliott, 23, was forced into surgery on the persistent injury after it failed to respond to rest and recuperation.

Boss Roy Keane told Sunderland's website: "It's not a major disaster, hopefully he'll come back stronger."

Meanwhle, director of scouting Bobby Saxton and chief scout Bob Shaw have both left the club in Keane's ongoing shake-up of his backroom staff.

Elliott will miss a crucial phase of Sunderland's promotion push, but Keane hopes to have the striker back for the run-in.

Keane said: "We hope he'll be back to finish the season well, his goals could be important for us."

I'm looking to bring in one or two of my own people Sunderland boss Roy Keane

Meanwhile, Keane continued to review his backroom staff, with the departure of Saxton and Shaw, and hinted there could be more changes.

Saxton leaves after six months of his second spell with Sunderland, having been brought back by chairman Niall Quinn to assist him before Keane's apppointment as manager.

Keane said: "It's one of those things in football. Bobby was a great help in my first few months at the club, but now things have settled down I'm looking to bring in one or two of my own people.