Today's Sunday Times reports that Sam has been carrying the problem for some time, preventing him from training properly and causing discomfort during matches. After putting off the operation as long as possible, he has been forced in for surgery and will be out for at least two to three weeks.
Colin Gregor, who had been included in the Heineken Cup squad as cover for both half-back positions, has a similar injury and is also unavailable, leaving Bevvy as the only fit scrum-half available for next week's Heineken Cup match with Northampton.
Glasgow also have problems in the front row with Euan Murray banned and Kevin Tkachuk and Lee Harrison leaving the field on Friday. It looks likely that Glasgow may have to call up one or more of the club props in their squad - Eric Milligan of Glasgow Hawks, Ben Prescott of Aberdeen and Elliot McLaren of Biggar
Competition rules mean that clubs must register their squads several months before the end of the qualifying period.
"In September, when we have to nominate our squad, we obviously have no idea who will be fit and able to play four months down the line," Hugh Campbell says in today's Sunday Herald.
"If Graeme Beveridge reports unfit we will have to go in against Saints without a recognised scrum-half - and at that stage I have no idea who would fill the slot."