Birmingham fear James McFadden faces a lengthy spell on the sidelines through injury.
The Scotland star suffered a knee problem during Tuesday's win over Derby and was forced off after 68 minutes.
McFadden is set to undergo scans with fears the forward could be sidelined for up to six weeks.
"I don't know how serious James' injury is," said McLeish.
"He's been hit in the medial ligaments so I don't know to what extent or if there is damage. He'll be scanned and we won't be able to tell for another 24, possibly 48, hours."
It means McFadden could miss Scotland's vital World Cup qualifier with Holland in March and George Burley is already drawing up a contingency plan if the former Everton man is ruled out of the trip to Amsterdam.
Burley admits Cardiff's in-form striker Ross McCormack is in the reckoning to fill in for McFadden if he does not recover in time.
"Ross is actively under consideration for the squad and Steven Fletcher, from Hibs, is another forward very much in my plans," Burley told the Daily Record.
"James McFadden has suffered a knee injury and you're never sure with these things. I've got my fingers crossed he'll be back, fit and available by the time we go to Amsterdam."