Wales international Dan Lydiate has been ruled out of the remainder of the season following a bicep injury.
The 30-year-old sustained the blow while playing for his club Ospreys in the 24th minute of the Pro 14 game against Dragons on Sunday.
Lydiate has been advised to undergo a surgery that will effectively rule him out of the upcoming Six Nations tournament for Wales.
Ospreys medical performance manager Chris Towers said: "After speaking to consultants and seeking specialist opinion, the decision has been taken in Dan's best interests to undergo surgery.
"That process will take place this week, ruling him out of consideration for the rest of the current season."
Wales are already without Sam Warburton while number eight Taulupe Faletau is recovering from a knee injury. Meanwhile, Jonathan Davies is another long-term absentee, having been hurt during Wales' November defeat against Australia.
Ross Moriarty's participation was also initially clouded with an injury concern but as a relief, to head coach Warren Gatland the 23-year-old could return to action this weekend after regaining full fitness.
Gloucester backs coach Tim Taylor told WalesOnline: "He's fit and training again and he will definitely be up for selection.
"It would be great to get him back involved over the next few weeks as well.
"He's fully fit now, he'll definitely get game time over the next four-week block."