Scott was injured in the pre-season game against Gloucester in August, while USA international Greg came off during the match against Ulster at Scotstoun last month.
Both players have commenced their rehab programmes and are expected to be unavailable for up to six months.
Namibian second-row Tjiuee Uanivi and centre Richie Vernon are having further investigations on shoulder injuries.
Meanwhile, Adam Ashe (hip/foot), Simone Favaro (shoulder), Chris Fusaro (knees) and Peter Horne (hand) are making good progress as they continue their rehab from injury.