Sunderland defender Wes Brown is likely to be sidelined for eight weeks by his knee injury.
The former Manchester United man damaged a knee during Sunday's FA Cup fourth-round 1-1 draw against Middlesbrough.
Manager Martin O'Neill said: "We don't think he needs the operation but you are looking at probably about eight weeks before he is back.
"But, at one stage, it looked like a season-ending injury."
Midfielder David Vaughan could also be missing for several weeks after damaging ankle ligaments during the same game.
O'Neill said: "David was feeling better today, but he is still very, very sore and the swelling is still up. We are looking at a few weeks for him."