Celtic skipper Scott Brown will be sidelined for up to two weeks after aggravating an ankle complaint during Sunday's 4-2 loss to Rangers.
The midfielder had to be withdrawn on 74 minutes and manager Neil Lennon said he would need to be "shut down".
"Scott was forced to come off during Sunday's derby game at Ibrox through injury," said a club statement.
"We are hopeful that the captain will be out of action for no more than a week or two."
Having missed the previous two matches with the same problem, Brown returned for the first Old Firm game of the season and set up Gary Hooper and Badr El-Kaddouri for their goals after Steven Naismith had opened the scoring for Rangers.
But he struggled after the break and when his injury flared up again he had to be replaced by James Forrest as goals from Nikica Jelavic, Kyle Lafferty and Naismith earned the home side victory.
"The ankle has gone again unfortunately," revealed Lennon.
"He felt fine before the game and looked great for an hour. It looks as if he is going to be shut down for a while until we can let it settle."
Brown played down the injury, saying: "I managed to hurt myself just a little bit but hopefully I will be okay."
The Scotland international was also defiant in defeat after his side slipped four points behind leaders Rangers in the Scottish Premier League.
"We are disappointed," said Brown. "But it is early in the season and there is still a lot to play for.
"I know we are four points behind but it (a comeback) has happened before.
"We gave it a shot but we didn't play as well as we could, we know we can do better.
"We were flying at half-time but we didn't come out for the second half.
"It is frustrating that we were in the driving seat then lost two early goals. But as I said before, it is early days."