Wales could be without star number eight Taulupe Faletau for this season's Six Nations.
Faletau's fellow 2017 British and Irish Lions Jonathan Davies and Sam Warburton are already sidelined as long-term injury absentees.
And Faletau might now join them after his club Bath said he faces a lay-off of 12-16 weeks with knee trouble.
With lock Jake Ball currently battling to overcome a dislocated shoulder, it means that Wales head coach Warren Gatland has suffered yet another blow almost two months out from the tournament.
Wales kick off their Six Nations campaign against in-form Scotland on February 3, followed by a Twickenham trip to face title holders England seven days later, then Ireland in Dublin on February 24.
A 12-week absence would rule Faletau out of Wales' first three Six Nations games, but the whole tournament could prove off limits for him with Wales also facing Italy on March 11 and then France six days later.
Bath have confirmed that 27-year-old Faletau suffered a grade three medial knee ligament injury.
The powerful number eight, who has won 70 caps and featured on the last two Lions tours to Australia and New Zealand, was hurt during Bath's European Champions Cup defeat against Toulon last Saturday.
It is understood that Faletau will see a specialist later this week to discover if surgery is required.