Newport Gwent Dragons captain Lee Byrne has been ruled out for "three to four months" after an operation on a torn shoulder muscle.
The Wales and Lions full-back, 34, has had a long-standing problem and went off during the Challenge Cup defeat to Newcastle in October.
Byrne moved to Newport from French side Clermont Auvergne in the summer.
"He's been outstanding for us in his leadership and playing ability," said Director of Rugby Lyn Jones.
"When Lee Byrne plays for us we're a different team.
"That's what you pay your money for and Lee can do things which not a lot of people can do.
"You'd be surprised what a good full-back can do for a team, what extra they can bring and he'll be missed.
"But that's the way it is. We need to get on with it and move forward."
Dragons lock Ian Gough and hooker Rhys Buckley have also undergone surgery, on shoulder and chest injuries respectively, and are expected to return early next year.
Lock Matthew Screech has returned to full training ahead of Friday's match against Munster at Rodney Parade after recovering from injury.
Utility back Hallam Amos is also available after being released from the Wales squad.
But Wales sevens player Rhys Jones is expecting to start at full-back after Byrne's injury.
"It's disappointing for Lee, he's a great captain and done well so far this season," said Jones.
"[But] starting in the Pro 12 against Munster is a great opportunity for me.
"I'm hoping to put a good performance in and hopefully keep that number fifteen jersey."
Dragons are currently 10th in the Pro 12 table after one win and six defeats from their opening seven games.