Martin O'Neill is hoping an injury picked up by Nicklas Bendtner on Saturday is not as serious as first feared, but admits the striker's fitness is a concern.
The Denmark international was forced off late on against Liverpool on Saturday.
He had earlier netted what proved to be the winning goal in that tie, with his close-range effort early in the second half helping the Black Cats to a 1-0 success.
His afternoon was marred after tangling with Martin Skrtel, with an unfortunate knock leading to him being stretchered from the field.
O'Neill claims it is too early to speculate on the severity of the injury, with it important for the club's medical staff to take a look at the striker before a timescale can be put on his recovery.
He is hoping that Bendtner can shake off the problem in time to face Everton in the quarter-finals of the FA Cup next weekend, but that may be a little optimistic.
"It is a knee injury," O'Neill told Sky Sports.
"I can't tell you much more at the moment. He's delighted to have scored the goal but he is very sore at the moment.
"We will get a scan in a couple of days and hope that he will be fit for next week.
"It is a concern."