Tua Tagovailoa left for the locker room in the second quarter of Sunday's game against the Buffalo Bills and was replaced by Teddy Bridgewater.
The Miami Dolphins quarterback sustained the injury when he fell backward to the turf on a shove by Bills linebacker Matt Milano. The back of his head bounced off the turf.
After standing up, Tagovailoa had trouble walking and fell back to the ground.
He then left for the locker room with the assistance of two trainers, and the Dolphins soon announced that he was questionable to return with a head injury.