Neil Lennon has confirmed that Joe Ledley will miss Celtic's match with Kilmarnock and is a major doubt for Sunday's derby with Rangers.
The midfielder picked up a hamstring injury in the Scottish Cup semi-final win over Aberdeen on Sunday.
Lennon admitted he was unsure how long the injury would sideline the Welshman.
"The medical staff are still trying to get a guideline," said the Celtic manager. "He could be out for a few weeks anyway."
Ledley has made 28 appearances for Celtic this season, scoring twice in the 2-1 Scottish Cup win over Inverness Caledonian Thistle last month.
When asked if he would consider risking the player against Rangers on Sunday, Lennon insisted that that would not be his preference.
"It depends on the extent of the injury," said Lennon ahead of Wednesday's meeting with Kilmarnock. "Hamstrings are delicate.
"It would be a massive gamble to put anyone in that sort of position with an obvious chance of him missing out for the remainder of the season.
"It's not a risk I would be willing to take."