Scotland lock Alastair Kellock will miss the Six Nations after undergoing surgery for an arm injury.
Glasgow confirmed that their captain would be out for about four months, after injuring his arm during their European Cup defeat against Cardiff at Scotstoun this month.
The 32-year-old has been a regular starter for the international team and joins fellow Glasgow and Scotland lock Jonny Gray on the sidelines.
Kellock, who has 56 caps for Scotland, wrote on his Twitter account: "Gutted about the arm but unfortunately part of the job I've had a good run for the last few yrs be back soon enough."
Glasgow head coach Gregor Townsend, whose team face Edinburgh on Boxing Day and New Year's Day, added: "We are all gutted for Al to be missing out on playing for the next few months, but especially the 1872 Cup games.
"He has played a prominent role in these games over the last few season and thrives against Edinburgh.
"We wish him well in his recovery and he still has a big role to play at the club as he works his way back to full fitness."
Meanwhile, X-rays have shown that Glasgow centre Mark Bennett has a fractured toe but will not require surgery.
Warriors say Bennett, who suffered the injury on Scotland Sevens duty, will be out for "several weeks".