The already anticipated news could be followed by one or two additional call-ups, but McLeish's squad is still 22 strong and the former Rangers boss may decide that is large enough.

The Celtic pair will miss the clash against Ukraine at Hampden on Saturday and then next Wednesday's match in Georgia.

Midfielder Hartley has a hamstring injury which is expected to keep him sidelined until the end of October.

From the moment he sustained the injury against Gretna on Sunday, Celtic were adamant it was serious enough to mean he would have to withdraw. Hartley's problem is understood to be a grade one injury, the least serious strain and one which requires around three weeks of rest for an injured player to recover from.

Defender Caldwell has knee and ankle problems, and although he got to the end of the Gretna match, he has since been in sufficient discomfort for Scotland to recognise he should be treated at his club rather than remain with the national team.

Hartley played a key role in a defensive midfield guise for Scotland in the shock 1-0 victory over France in Paris last month and might have expected to keep his place.

McLeish's midfield options are becoming limited with Manchester United's Darren Fletcher also out due to injury and suspension.

While Barry Ferguson, Lee McCulloch and Scott Brown appear certain starters, it will be left to fringe men Barry Robson, Gary Teale and Stephen Pearson to contest the fourth place in midfield.

McLeish also has the option of selecting three strikers, with one - perhaps Shaun Maloney or James McFadden - playing in a wide role.

The loss of Caldwell means Scotland will have reduced cover in central defence, with Christian Dailly the only natural cover for Stephen McManus and David Weir.

With Sunderland's Russell Anderson also injured, McLeish is not blessed with options, although Celtic's John Kennedy is a player the manager may consider inviting to replace his club-mate in the squad.