Jordan Willis will be out of action for three weeks after receiving an injection to ease his knee injury.
Sunderland's medical team has been working with the centre-back to manage a long-term patella tendon problem and they made a plan several weeks ago to give him the injection this week, knowing he would be needed to play against MK Dons last Saturday while Tom Flanagan and Conor McLaughlin were away on international duty.
And Phil Parkinson confirmed that Willis has now had the treatment, and will need to rest his knee for three weeks before he is able to return to Sunderland's League One campaign.
"Jordan had his injection on Wednesday," said Parkinson, whose side travels to face Doncaster Rovers tomorrow.
"To get the best out of Jordan going forward, we felt it was the right thing to do and of course we have Conor and Tom coming back into the squad this weekend against Doncaster.
"Jordan will probably out for three weeks now. If we can give him three weeks' rest there will be more benefit for him.
"In the last couple of games he has done well, but he has been taking painkillers before playing and the other day he said he was struggling towards the end of the game.
"So he has had it done and we move forward without him, although we are looking forward to him coming back."
Parkinson also has one or two players nursing minor injuries in the build-up to the Doncaster game, with Luke O'Nien and Aiden O'Brien on that list.
He said: "We haven't got any major additional injuries, aside from those we had going into the MK Dons game.
"There are one or two niggles - Luke took a whack in training and we'll need to see how he is, and Aiden has a slightly tight groin."
Goalkeeper Lee Burge missed the MK Dons game due to a minor ankle problem but is expected to be fit to return tomorrow.
And there was some good news for Parkinson with wingback Callum McFadzean returning to training today after picking up a hamstring problem in Sunderland's EFL Trophy tie at Fleetwood Town ten days ago, although his lay-off means he will not go straight into the squad tomorrow.
Parkinson said: "Callum was back out on the training pitch today.
"His hamstring injury took a little bit longer than we first anticipated, but we felt it was important that we gave him enough time to recover fully rather than rush him back, and he is training again now."
