Edinburgh and Scotland lock Grant Gilchrist has suffered another injury setback.
The 25-year-old has had to undergo surgery on the groin injury which ended his World Cup prematurely.
No timescale has been put on his recovery but Gilchrist now faces a challenge to be fit for the start of the RBS 6 Nations campaign against England on February 6.
A statement from Edinburgh read: "Following Grant's groin injury during Rugby World Cup, his rehabilitation was proceeding smoothly.
"As part of his rehabilitation the area was scanned again. Further specialist opinion revealed some damage to soft tissue structures which had not previously been clinically evident.
"Following best advice from the specialist, it was decided that surgery would be the most appropriate course and this has already taken place.
"Grant will continue with his recovery now under the care of the Edinburgh Rugby medical team."
Gilchrist was named Scotland captain ahead of last year's November Tests but soon suffered an arm injury which ruled him out for the rest of the season.
And his World Cup ended during Scotland's second game, when he was injured against the United States.
Gilchrist is one of 13 players unavailable to Edinburgh head coach Alan Solomons for Friday's Guinness pro12 fixture against Ulster, a list which now includes Greig Tonks (hamstring), Sam Hidalgo-Clyne (hand), Fraser McKenzie (neck) and Tom Brown (shoulder).
They drop out of the squad for the Belfast clash but winger Dougie Fife returns from injury while Jack Cuthbert, Sean Kennedy and Anton Bresler come in.
Solomons said: "Ulster at the Kingspan in front of a home crowd will be a tough ask, without a doubt, and we have to make sure that we are at our best. This will be a real test for the team, and especially for our strength in depth, bearing in mind our heavy injury toll."