Scotland have received a triple injury blow ahead of their autumn Test series, which features games against New Zealand, South Africa and Canada.
Experienced Lion Chris Cusiter will miss those games, being ruled out for six weeks after fracturing a thumb.
Fellow scrum-half Rory Lawson will see a specialist after picking up a rib cartilage injury, while centre Graeme Morrison has knee ligament damage.
Mark McMillan has been called into Scotland's training camp squad.
The 25-year-old uncapped Glasgow Warriors scrum-half, who is a former national under-21 captain and represented Scotland A during the summer, flew out with the home-based players from Edinburgh Airport on Sunday for this week's warm-weather camp in Spain.
Scotland face New Zealand on 8 November, South Africa seven days later and then Canada on 22 November.
In another development, Ospreys have now agreed to release their Scotland winger, Nikki Walker.
Should he come through unscathed from his club's match on Sunday against Worcester, he will join up with the Scotland squad on Monday.
But the squad is minus Cusiter after the Lion broke a thumb while playing for Perpignan against Dax on Saturday, an injury that will require surgery.
Lawson, who acted as understudy to captain Mike Blair on the summer tour of Argentina, suffered his injury in Gloucester's match against Dragons and will see a specialist on Tuesday.
Glasgow Warriors' Morrison was deemed not fit to travel by Scotland team doctor James Robson.
He picked up his injury in Glasgow's Magners League victory over Leinster on Friday.
Morrison, who scored the decisive try in Scotland's historic first-ever Test victory in Argentina in June, will now undergo further assessment and daily treatment from the Glasgow medical staff.
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