Glasgow second-row duo Scott Cummings and Greg Peterson have both been ruled out for six months after undergoing shoulder surgery.
Cummings was injured in Warriors' pre-season clash with Gloucester in August, while USA international Peterson was hurt during the Scotstoun side's Guinness PRO12 match against Ulster last month.
A Glasgow spokesman said the pair will now be unavailable to head coach Gregor Townsend until well into the new year.
He said: " Both players have commenced their rehab programmes and are expected to be unavailable for up to six months."
Meanwhile, Namibian second-row Tjiuee Uanivi and centre Richie Vernon are having further investigations on shoulder injuries.
However, Warriors say Adam Ashe (hip and foot), Simone Favaro (shoulder), Chris Fusaro (knees) and Peter Horne (hand) are making good progress as they continue their rehab from injury.