Scotland and Glasgow prop Moray Low faces at least two months out with a knee injury picked up at Scarlets.
The injury means Low, selected for the Six Nations squad, will miss at least the start of this year's tournament.
However, club and country team-mate Ruaridh Jackson, injured in the same match, should return to action shortly.
"This is clearly very disappointing news for Moray, and the injury has come at a very unfortunate time," said Glasgow head coach Sean Lineen.
"He's a tough character, however, and I know he'll work hard to bounce back strongly."
Low has had an injury-plagued season, with a calf injury ruling him out after his return from the World Cup, where he was the only Scot not to feature.
After returning to the Warriors lineup at the end of November, Low scored the only try in Glasgow's 17-12 victory over Edinburgh in the 1872 Cup match at Firhill.
Both players came off in the first half of the RaboDirect Pro12 League defeat to Scarlets in Llanelli.
But, while no long-term issues are expected for 23-year-old Jackson, who had a thigh problem, Low has suffered damage to his medial collateral ligament.
Scotland head coach Andy Robinson was hopeful Jackson would have no problem ahead of the start of the Six Nations training schedule.
"We all wish Moray a speedy recovery," he said.
"As far as Ruaridh is concerned we will be monitoring his progress closely before the players come into camp with us later this month."