The Panthers made room on the 53-man roster Tuesday by waiving running back Andre Brown a week after claiming him from Indianapolis.
Clausen, who took over as the starter after Matt Moore's season-ending shoulder injury, sustained a concussion late in Sunday's loss to Tampa Bay. If he can't play against Baltimore, fellow rookie Tony Pike would make his first NFL start.
The only other QB was rookie Armanti Edwards, who has been playing receiver outside a few wildcat snaps.
The 30-year-old St. Pierre has thrown five NFL passes, completing two for 12 yards with a touchdown and an interception.