Celtic captain Scott Brown is to undergo ankle surgery and will be out for up to 10 weeks, the club have confirmed.
The midfielder initially sustained the injury while playing for Scotland in August and has missed the last four games for his club side
He will now have "a minor procedure" on the joint, handing another headache to Celtic boss Neil Lennon.
His side currently lie third in the league, 10 points behind Rangers.
Meanwhile, Joe Ledley has withdrawn from the Wales squad with a mild groin strain but is expected to train next week in hope of being ready for Celtic next Scottish Premier League tie against Kilmarnock on 15 October.
Adam Matthews, who came off against Hearts on Sunday, has joined up with the Wales squad where his fitness will be assessed.