Goalkeeper Allan McGregor is the latest player to withdraw from Scotland's World Cup qualification double header.
The 31-year-old, capped 30 times, was already going to miss the Belgium game due to suspension, but injury means he will play no part against Macedonia
It follows the withdrawal of George Boyd, James Morrison and Graham Dorrans on Monday.
Manager Gordon Strachan called up Craig Bryson, Chris Burke, Kevin Thomson and Lee Wallace to increase his options.
The Scots host Belgium on Friday before facing Macedonia the following Tuesday.
Morrison withdrew with a groin problem while Dorrans's injury has not been disclosed. Boyd withdrew from the squad due to an ankle injury.
Derby County's Bryson, Birmingham City winger Burke, Hibs midfielder Thomson and Rangers defender Wallace will all hope to feature in the qualifiers.
Barry Bannan is not currently with the squad, but he should join up with his team-mates on Tuesday.
Thomson expressed delight at his call-up, three years since his last involvement with the national side.
"A return has always been a big personal goal for me," the three-time capped midfielder told his club website.
"Obviously I've squeezed in through other boys' hard luck and injury, although I've experienced that side of it before too.
"Hopefully this will be start of what will be a good season for me. To be back involved is great and even if I don't get to play in either of the qualifiers it's a special feeling to be part of the Scotland squad again."
West Brom midfielder Morrison, who scored in Scotland's 3-2 defeat by England, suffered a groin injury in Sunday's defeat by Swansea.
"He felt a pain in his groin just before half-time, the last couple of minutes in the first half," said Albion boss Steve Clarke.
"The medical people will assess it but I would imagine he is doubtful for the Scotland trip."
Scotland currently sit in fifth place in qualifying Group A with five points from seven games.