Jack Ross has confirmed that Duncan Watmore suffered a 'slight groin injury' against Newcastle United U21s.
Watmore was replaced at half time after struggling in the latter stages of the opening 45.
The Black Cats ended up winning 4-0 but Watmore is now an obvious doubt for the visit of Luton Town this weekend.
Ross was relaxed about the setback and said that he would not take any chances with the 24-year-old.
"It's just a slight groin injury," Ross said.
"Not unexpected given the length of time he has been out of the game. It quite often happens.
"We also have a duty of care to him that we would never take any chances with him.
"I'd rather be out for a week than four, mentally for him as well.
"We'll assess him in the morning and see how he is.
"We didn't want to take any risks with him."
Watmore has made eight appearances since making his return early last month.
Ross also confirmed that Sunderland are set to announce the signing of Jimmy Dunne.
The Irish defender has impressed on loan at Hearts in the first half of the season and was recalled by the Premier League side this week.
He is now set to join the Black Cats and boost Jack Ross's options.
"I would hope that in the next 24 hours we would be able to confirm an addition defensively," Ross said.
"I've always said, until it's done, dusted, registered [I'll be cautious] but I'm hopeful that will be the case."
Chairman Stewart Donald said on Tuesday that the Black Cats were also hoping to bring in a striking addition 'relatively quickly'.
They have been linked with Wigan Athletic's Will Grigg.