Alun Wyn Jones will need at least 10 weeks to recover from his knee injury, Ospreys fear, putting his involvement in Wales' Six Nations opener in doubt.
Wales captain Jones - Test rugby's most capped player - sustained the blow in his side's Autumn Nations Cup win over Italy.
That victory was on December 5, nine weeks out from the start of the 2021 Six Nations, where Wales begin their campaign against Ireland on February 7.
That clash could therefore come too soon for Jones, according to Ospreys coach Toby Booth, although he expects the 35-year-old will work to return ahead of schedule.
"We've spoken to the powers that be in relation to his knee," Booth said, discussing the lock ahead of his team's European Challenge Cup encounter with Worcester Warriors.
"We think he will be double-figure weeks.
"If I said it to Alun, he would say, 'I will be back in eight'. That's the nature of the beast.
"He is probably going to be somewhere around that sort of timeframe, which is disappointing for him and obviously for us.
"If anyone is going to get back early, it will be him."
Jones matched Richie McCaw's total of 148 caps against France in October, claiming the outright record a week later in the defeat to Scotland.
