Goalkeeper Paul Smith has been taken to hospital after being knocked out during his side's 1-0 defeat at Gillingham on Tuesday night.
The 32-year-old custodian received eight minutes of treatment on the pitch after clashing with Gills striker Deon Burton.
And Blues boss Paul Sturrock revealed after the match that Smith was undergoing checks for concussion.
“Paul was knocked out cold for a little while but thankfully he did come back round before going to hospital,” said Sturrock.
“He's being checked for concussion and he's very doubtful for Saturday's game with Exeter.”
Mark Phillips is also likely to miss out on facing the Grecians after Sturrock confirmed the centre-back had been forced off just before half-time with a serious groin problem.
“Mark looks like he's picked up a bad groin problem,” he added.
“We're not sure how long he will be out for but it doesn't look too hopeful for the weekend.”