He has been taken to hospital to undergo scans.
Brown was involved in a four-man collision mid way through the quarter and was taken off on a medicab wearing a neck brace.
The ball was pumped into the Lions forward line where Brown ran back with the flight of the ball into the oncoming traffic with eyes only for the ball.
He collided at full speed with Geelong's Harry Taylor and teammate Mitch Clark coming the other way and was instantly knocked out, laying prone on the ground.
Clark was also dazed and taken from the field while Brown's opponent Tom Lonergan got up unscathed.
Brown was substituted for Ryan Harwood.
It was the second time this season that Brown has been involved in a terrible collision.
He missed eight matches after an accidental knee from Fremantle's Luke McPharlin in round one caused multiple facial fractures.
