Southampton's Danny Fox and Charlie Mulgrew of Celtic, who would be expected to contest the position, reported to Scotland's training camp with injuries yesterday.
Russell Martin, the Norwich City defender, is also a doubt and Christophe Berra, the Wolverhampton Wanderers centre-back, was excused as he awaits the birth of his first child, due today.
Peter Houston, the assistant manager, said: "Fox has a groin strain, Martin has an ankle knock and Mulgrew's Achilles is still a bit sore after he missed Saturday's game for Celtic.
"The good thing is we have got a few days. Sometimes injuries settle down after 48 hours. We'll keep everyone informed."
Houston admitted that if the players had not recovered by today or tomorrow, reinforcements may have to be brought in. With Phil Bardsley, the Sunderland full-back, recovering from an ankle injury, there is Scotland short of left-back options hardly a host of left-backs pushing their way into Levein's thoughts. The inclusion of Lee Wallace, of Rangers, remains a possibility, if a distant one.
There was good news for Scotland, however, with Allan McGregor, the Besiktas goalkeeper, expected to play after recovering from the groin strain that forced him off in the friendly win over Australia last month.
"He played on Saturday and kept a clean sheet," Houston said. ''It's a huge bonus to us that he's fit and available. He's one of the best goalies about and you don't realise how good he is until you work closely with him.''
Houston added: ''It makes a huge difference to the defence that he's there because of his experience of top-level matches with Rangers and Scotland. Confidence comes from having somebody strong behind you and Allan's up there with the best of them.''
Scotland go into the match against Serbia on Saturday without Steven Fletcher, who repaid some of his £14m fee when hitting a double for Sunderland on his Barclays Premier League debut for the club in a 2-2 draw at Swansea on Saturday.
The former Wolverhampton Wanderers and Hibernian striker has been involved in a stand-off with Levein for 18 months despite attempts to repair the breach.
But Houston said Scotland were well-covered in the striking area. ''You look at Jordan Rhodes, who has been in excellent form and got an £8m move," he said of the forward who moved last week from Huddersfield Town to Blackburn Rovers.
"Kenny Miller has settled in well in the USA and another lad who has been with us, [Craig] Mackail-Smith, who didn't make the squad, his two goals were absolutely sensational at the weekend. Ross McCormack also scored in the Championship. There are guys who are naturally good goalscorers."
Houston also said there had been no movement over a new contract in his job at Dundee United.
He said: "I haven't had an offer, so there is nothing to say. To refuse an offer you've got to be offered one. But at this moment in time it is not something I am worried about."
Big match build-up. Pages 2-5
world cup qualifying Injury worries ahead of Hampden double-header
Contextual targeting label: