Kris Boyd is the latest player to withdraw from the Scotland squad ahead of Friday's friendly against the Czech Republic in Prague.
The Rangers striker is struggling with a hamstring strain and becomes the fifth withdrawal confirmed in the last 24 hours.
As well as Boyd, Ibrox team-mates Kevin Thomson and Steven Whittaker are out, along with James McFadden and Alan Hutton, with a calf injury and infected toe, respectively.
Hibernian's Steven Fletcher has also failed to train with a chest injury, while stand-in skipper Stephen McManus is struggling with a groin strain.
Manager George Burley said on Tuesday: "Boyd was here this morning but he has a tight hamstring so he will not be available.
"Steven Fletcher didn't train because he had a bang on the chest on the last day of the season, while Stephen McManus has a groin strain. But he is very keen to play so hopefully he will be fit."
As for the withdrawals, Burley added: "It's happened and it gives others an opportunity and, if they take their chance, they will be in pole position for the World Cup qualifiers.
"It's frustrating but maybe it comes with the territory. There is nothing we can do about it so it's a case of pushing on."
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