Neil Lennon is unsure whether midfielder Joe Ledley will be fit for Sunday's Old Firm clash with Rangers at Ibrox.
The former Cardiff City man damaged his hamstring in their weekend Scottish Cup semi-final win over Aberdeen.
The Wales international will miss Celtic's midweek clash with Kilmarnock and he remains doubtful to feature against Gers.
Lennon is keen to resolve the issue as soon as possible, although he accepts that any sort of gamble could backfire by ruling him out for the remainder of the campaign.
"He is definitely out of (Wednesday) night and he is a huge doubt for Sunday," said Lennon. "We don't know how long he is going to be out for at the moment.
"It is a niggle of some sort and the medical staff are still looking at it and trying to get to the bottom of it, to give us some guidelines.
"Hamstrings are a very delicate injury and it would be a massive gamble with the obvious chance of it tearing and him being out for the remainder of the season.
"It's a not a risk I would be willing to take on a player who has been very influential and who we need for the run-in."
Fit-again defender Daniel Majstorovic made his comeback from a fractured toe in their semi-final success at Hampden Park.
The veteran Swede was naturally delighted to be back in action and he is now looking to feature in their upcoming games against Kilmarnock and Rangers.
"The body felt good and of course it's good to return to the pitch," he told Fotbollskanalen.se. "The rehab went well, but it's no fun being away as long as I was.
"Of course it takes time to be 100 per cent after something like this. Physically it feels okay, but I need to regain my pace and fitness, but that shouldn't be a problem.
"We have another game on Wednesday. It's an important game. We're two points ahead with six games left. They've played a game more, but of course the Old Firm game will be decisive."