But Clarke Carlisle is on course to shake off a back problem to face Alex McLeish's men.

Duff had to withdraw from the Northern Ireland squad with a side strain suffered in the 3-1 defeat at Reading on Saturday, incurred trying to prevent Stephen Hunt heading in the Royals second goal, before being replaced by Chris Eagles just before the hour.

And Carlisle visibly struggled in the second half of the game at the Madejski Stadium, particularly for the third goal, when Kevin Doyle beat him to the bye-line to cross for Shane Long to score.

Boss Owen Coyle said after the game: "Clarke played after struggling with his back, and his movement was limited."

And he updated the pair's progress yesterday: "Clarke's back has eased up a bit, but Michael is more of a concern.

"He has been undergoing treatment all week, and we will see how we responds to that."

With Russell Anderson expected to miss the rest of the season with cruciate knee ligament damage, and Stephen Jordan, harshly sent off at Reading in injury-time, suspended against Birmingham, the last thing Coyle needs at this moment in time is further defensive headaches in a department thin on the ground.

But with Christian Kalvenes a like-for-like replacement for Jordan, and Graham Alexander able to play either full back position, he does have options.

With the two-week international break, Coyle arranged a behind-closed-doors game at Gawthorpe on Wednesday against Blackpool to give some of his squad some match practice.

Ade Akinbiyi, who has played only 104 minutes so far this season, Alan Mahon, who has played 49, Chris Eagles – who has made a big impact off the bench in the last four games, after missing three through suspension, and Diego Penny, who has not featured since the opening day of the season, all got some minutes under their belt.

And although Mahon and Penny both picked up slight knocks, but Coyle admitted: "They are nothing to be unduly worried about."

He added: "The boys worked hard, and it was good for a few of them to get a game."

Coyle will be at Hampden Park tomorrow to check on Graham Alexander, should he be called upon by George Burley for Scotland in their World Cup Group Nine qualifying clash with Norway, while also running the rule over Birmingham's James McFadden.

The game is live on Sky Sports 1 (kick-off 3 p.m.).