Celtic could be without midfielder Beram Kayal for up to four months after it was confirmed he requires ankle surgery.
It was initially thought the Israel international would only miss one month after picking up the injury in last week's 1-0 win over Rangers.
A specialist requested a second set of scans one week after the initial diagnosis where it has been confirmed the 23-year-old needs to undergo an operation.
Manager Neil Lennon confirmed the news and Kayal is booked in for surgery in London on Monday with Celtic set to make a further announcement next week.
"He had a second scan and he needs surgery," confirmed Lennon.
"We don't know what the outcome of the surgery will be. There's a possibility that he could be out for four months.
"It would be a huge blow for me and the player and the club itself.
"He is a pivotal player for us. But I will say one area we have real quality strength in depth is midfield. I've got plenty of cover in midfield.
"But no-one likes to lose a player for a concerted period of time. We have been unfortunate with these injuries."