With 3:09 to go in the first quarter, Thorson was hit by Carl Nassib after completing a 13-yard pass to Christian Jones. Thorson stayed down and was taken out after suffering a lower-body injury, replaced by Zack Oliver.
Coach Pat Fitzgerald didn't provide an update on Thorson's status, quipping that his quarterback was feeling ''ecstatic'' about the win.
Northwestern ended up winning 23-21.
Thorson entered Saturday's game with 1,119 passing yards and six touchdown passes.