The summer signing from Fleetwood Town has started every one of the Foxes’ 10 league games so far this season, but has been absent from training in recent days.
And while refusing rule him out entirely, Pearson has doubts over whether the Sheffield-born striker, who has scored four times this term, will be able to maintain his ever-present record in the Foxes starting eleven at St Andrew’s.
“Vardy hasn’t trained, he’s been ill,” Pearson told the media on Thursday.
“There’s a doubt as to whether he will be involved at the weekend because he’s been off for a few days now.
“It’s a bit unfortunate, but if he’s not available someone else will get an opportunity.
“I’m not completely ruling him out yet, we’ll see how he is tomorrow.”
Vardy, 25, has started 11 games for City in all competitions this season following his summer move from Fleetwood, scoring four times.
Saturday’s game at Birmingham sees Leicester going in search of a sixth successive win in the npower Championship, as they look to strengthen their position among the division’s early pace-setters.