Duncan Watmore has been ruled out for eight to 12 weeks with ankle ligament damage and is set to miss the rest of the season.
Watmore was injured in the 1-1 draw with Wycombe Wanderers at the end, the victim of a late challenge by Marcus Bean, who was shown a second yellow for the awful challenge and misses one game as a result.
For Watmore, the damage was much more serious and he will now face three months out injured, effectively ruling him out for the rest of the campaign.
Speaking after the goalless draw at Oakwell with promotion rivals Barnsley, Jack Ross said: “Duncan will most likely miss rest of the season.
“We are looking at 8-12 weeks timescale, even if he comes back before the end he will find it difficult to get up to speed.
“If there is a positive then his knee feels strong and well. It’s a blow for him and us.
“We are also missing Chris Maguire in the forward positions. I know Barnsley have found it as well, how you can have a full squad and then suddenly someone.It can change very quickly but we have showed that we have enough in our squad to cope with the challenges.
“It’s ankle ligament damage.
“As a manager you can’t just say he’s great, I have always said players are human beings.
“To use a Scottish phrase, he is scunnered, he is fed-up, he has worked for two years out the game to get back.
“He has been in a good place. There’s nothing wrong with feeling that way.
“He then has to deal with it and he is a positive guy anyway.
“The positive is his knee feels strong. We weren’t pleased with the tackle at the time and that is what happens sometimes.”
Sunderland are without skipper George Honeyman for the next two league games through suspension, while Tom Flanagan missed the draw at Oakwell with concussion.
Chris Maguire is also out with a fractured fibula, with Reece James missing with a groin strain. Sunderland host Walsall at the Stadium of Light on Saturday.