Hleb sustained a knee injury in the 3-0 FA Cup win over Sheffield Wednesday this weekend.
Blues boss Alex McLeish said: “Alex is limping heavily. He will have a scan hopefully over the next 24 hours.”
“It is his knee,” said McLeish. “We don’t believe there is any cruciate problems but he got a fair rattle. The guy was very late in the tackle.
“We presume we can get something done on Sunday and we will know after that if there is any damage.
“He is a great player and we still believe he will make an impact for us at some stage this season and, hopefully, he will be OK for the final.”