Celtic manager Neil Lennon will not risk Joe Ledley in Sunday's Old Firm clash with Rangers at Ibrox.
The Hoops midfielder will definitely miss Wednesday night's Clydesdale Bank Premier League game at Kilmarnock with a hamstring injury sustained against Aberdeen in the Scottish Cup semi-final win at the weekend.
And the Celtic boss has also all but ruled the Welshman out of the trip to Govan, saying: "He is definitely out of tomorrow night and he is a huge doubt for Sunday."
He added: "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."
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