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.