Scotland hooker Fraser Brown could miss the autumn Tests after surgery on an injured ankle.
He is likely to take up to four months to recover, and Scotland face Samoa, New Zealand and Australia in November.
The injury is a further setback to Scotland head coach Gregor Townsend, since Stuart Hogg and Jonny Gray are also likely to miss the Tests.
Hogg had surgery on a shoulder problem while Gray had an operation for an injured wrist.
Brown featured in all three of Scotland's summer tour matches - the first games of Townsend's Scotland reign. The 28-year-old was a replacement against Italy and Fiji, and started the 19-24 victory over Australia in Sydney.
All three Glasgow Warriors players will miss the opening rounds of the Pro12 and the European Champions Cup.
The remainder of the Warriors' Scotland internationals returned to training after being granted an extended rest period, although British & Irish Lions winger Tommy Seymour will continue his break until next month.