Sunderland's Carabao Cup win against Sheffield United came at a cost with the Black Cats waiting to learn the extent of Elliot Embleton's injury.
Boss Jack Ross hopes the 20-year-old's hamstring problem is not as serious as the one that ended his successful loan spell at Grimsby last season.
Embleton had to be withdrawn at half-time in the 1-0 victory at Bramall Lane on Wednesday night.
"He's a bit upset because it's his hamstring again," said Ross. "First impressions are that it's not as bad but it's not a straightforward one.
"I've been really impressed with him this season, people may argue about the game time he's had but he's still had a good chunk and been around the squad.
"This was a chance to show how good he is and he did that. I'm really disappointed for him, we'll look after him and when he's fit and ready he'll come back into the squad."
Max Power's superb 25-yard strike won the third-round tie for Sunderland but Ross was pleased with a first clean sheet of the season and the debuts of Laurens De Bock and Joel Lynch.
"Laurens did well to last the game because we weren't sure if he would because he is a bit behind Joel in terms of fitness," said Ross. "He is a proper left-back and you could see that, and we need that.
"I was really pleased with Joel, when you recruit so late in the window players tend not to have had a proper pre-season with much game time so he has worked hard to get himself up to speed.
"He is different to the other central defenders we have got – he is a natural left-sider for a start. He also has a presence about him and, it might not be obvious from the stands, but he is a real organiser as well."
Sheffield United boss Chris Wilder immediately turned his attentions to the visit of Liverpool in the Premier League on Saturday.
He said: "The games come round thick and fast for us now and we move on. We've got the European champions coming to Bramall Lane and we need to prepare for that. We will need to be at our very best if we are to get a result."
