Wales captain Alun Wyn Jones faces a race against time to be fit for the Six Nations, with Ospreys head coach Toby Booth predicting on Thursday that he could be out for at least 10 weeks.
The 35-year-old Ospreys lock -- Test rugby's most-capped player -- suffered a knee injury during Wales' Autumn Nations Cup victory over Italy earlier this month.
Booth said Jones' absence could be "double figures" in terms of weeks from when he was injured.
Wales kick off their Six Nations campaign at home to Ireland on February 7, which is followed by a Murrayfield appointment with Scotland six days later.
Speaking ahead of Ospreys' European Challenge Cup game against Worcester on Saturday, Booth said: "We've spoken to the powers that be in relation to his knee.
"We think he will be double-figures 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 time-frame, which is disappointing for him and obviously for us.
"If anyone is going to get back early, it will be him."
It is a major concern for Wales head coach Wayne Pivac, who has overseen just three victories in 10 Tests since succeeding Warren Gatland last year.
Jones joins a list of injured Wales players. Scarlets trio Liam Williams, Johnny Williams and Ken Owens are all currently sidelined, along with Dragons back-row forward Ross Moriarty.