Scotland face issues in central defence after Charlie Mulgrew dropped out of the squad for their opening Euro 2020 qualifiers.
Aberdeen centre-back Scott McKenna also emerged as an injury doubt for the games against Kazakhstan and San Marino after playing through a thigh injury on Saturday.
Mulgrew was one of three players to drop out along with Millwall goalkeeper Jordan Archer and Sheffield Wednesday midfielder Barry Bannan.
Livingston goalkeeper Liam Kelly and Kilmarnock centre-back Stuart Findlay have been handed first call-ups.
Blackburn skipper Mulgrew has missed his club's last two games after suffering a hamstring injury.
And Aberdeen boss Derek McInnes cast major doubt on McKenna's participation for Thursday's Group I opener against Kazakhstan in Astana after the 22-year-old played with a heavily-bandaged thigh during his team's 1-1 draw with Livingston.
McInnes said after the match: "He wasn't fully fit but with Andrew Considine failing a fitness test with his calf, he had to go in. He'll be a doubt for the Scotland game.
"If he does travel, I'm not sure he'll be fit for that first game. The tightness of the thigh, the travelling, the astroturf pitch. I wouldn't want to rule him out – I'm not a medical expert.
"We need to make a decision between us and Scotland whether he travels."
Findlay was a Scotland Under-21 regular and has impressed under Steve Clarke at Kilmarnock. The other two centre-backs in the squad are John Souttar of Hearts and Hamburg's David Bates.
Archer was dropped from the Millwall team for the midweek victory over Birmingham and was not in the squad for Sunday's FA Cup quarter-final defeat to Brighton.
Bannan – who has not featured under Scotland boss Alex McLeish – played the full 90 minutes and set up three goals as Sheffield Wednesday beat Blackburn 4-2 on Saturday.
There was better news for McLeish as key midfielder Callum McGregor played the full game as Celtic beat Dundee 1-0. The 25-year-old had been missing for four matches with a calf problem.
