Birmingham are concerned about the fitness of key midfielder Craig Gardner ahead of Saturday's home clash with Chelsea.
Gardner, City's leading scorer with four goals this season, suffered an ankle injury during last weekend's goalless draw at Manchester City.
The former Aston Villa player, 23, has seen a specialist this week and Blues boss Alex McLeish is waiting anxiously on the results.
Gardner has been one of Birmingham's most consistent performers this season with his energy and attacking runs. He forced his way into the side at the expense of Lee Bowyer, who formed an effective partnership with Barry Ferguson last season.
City badly missed Gardner's drive when he had to serve a three-game ban for being sent off against Wigan. He suffered the latest setback in a challenge with City midfielder Nigel de Jong during the first half.
If he is ruled out, then the experienced Bowyer, who replaced Gardner at Eastlands, is favourite to earn a recall.
Birmingham will look to improve on a record of only three wins in their last 22 Barclays Premier League games when they face Carlo Ancelotti's side.
Meanwhile, Birmingham could have Ben Foster as their only goalkeeper for the Carling Cup quarter-final against Villa on December 1.
Number two Maik Taylor is still struggling to overcome a shoulder injury which has ruled him out of the last two games.
The club's only other senior goalkeeper, Colin Doyle, will be cup-tied as he played in the competition for Coventry when on loan earlier in the season.