Chris Coleman has revealed midfielder Darron Gibson has a groin injury that he is having to carefully manage.
Gibson, who Coleman describes as Sunderland's 'best passer', has had the problem all week and was restricted to 75 minutes against Birmingham City.
The Republic of Ireland international, a key player in recent weeks given the midfield injury crisis Coleman has had to deal with, will be assessed ahead of the trip to Sheffield United on Boxing Day.
Sunderland made a triple substitution with 15 minutes to go, Gibson, Lewis Grabban and James Vaughan replaced by Didier Ndong, Joel Asoro and Josh Maja.
Coleman revealed: "Darron Gibson has got a groin problem, he has had a tough week. With the games coming up we couldn't risk him any longer than we did.
"He is one player you want on the pitch, he is our best passer. We couldn't risk him any longer than we did.
"I hope he won't miss Boxing Day. We have to see how he settles down.
"We haven't got Lee Cattermole, Paddy McNair, Didier Ndong this was only his second game back and couldn't really play any longer than he did.
"Holding midfield players are scarce at the moment. With these games coming thick and fast, it will be seeing where we are in 24-hours to see if players are ready.
"Who feels the best, really."
Coleman stressed after the Fulham win last weekend that he wasn't getting too carried away, with Sunderland back in the drop zone after the draw with Birmingham City.
The Sunderland boss added: "I never for one moment thought last week had solved all our problems.
"It was a nice step forward for us. If last week hadn't happened maybe we wouldn't have come back from 1-0 down against Birmingham and instead went into our little shell and hoped our problems go away.
"Last week was a great win, brilliant for everyone, it was a step forward but not the answer to all our problems.
"We have a lot of work to do. It will take a huge, brave effort from all of us."