Steve Clarke has handed David Bates and Mikey Devlin late call-ups to the Scotland squad after injuries.
It comes as Grant Hanley and Liam Palmer are ruled out of the double header against Belgium and Russia.
It means Scotland now have four centre backs in the squad with the pair joining Charlie Mulgrew and Liam Cooper.
But Bates and Devlin have played just three games between them this season with the Aberdeen defender suffering an injury in July.
He then struggled to get back in the team until Saturday's win over Ross County while Bates has played just once since his move to Sheffield Wednesday from Hamburg.
That came last midweek against Rotherham in the Carabao Cup and he was back on the bench as an unused sub against QPR.
His team-mate Palmer was replaced with 15 minutes to go and has now been ruled out with an injury.
Record Sport revealed on Saturday that Hanley was also set to be ruled out after picking up an injury in Norwich training.
He wasn't in the squad as his side were beaten 2-0 by West Ham.
