Coach Kyle Shanahan said after the 49ers' loss that Cannon, who was in stable condition, would stay overnight at a hospital for observation but that he had been cleared from other injuries aside from the concussion.
Cannon, who is one of San Francisco's primary special teams players, was chasing down Seahawks returner DeeJay Dallas when he collided with 49ers safety Talanoa Hufanga. On the play, Cannon attempted to tackle Dallas from one side as Hufanga converged from the other.
Both Cannon and Hufanga missed Dallas, and Hufanga's left thigh hit Cannon in the head as his neck bent backward. Cannon stayed on the field for minutes as medical personnel tended to him. After bracing Cannon's neck, medical officials removed his face mask, and he was loaded into an ambulance and taken off for further evaluation.
Soon after, Cannon was ruled out for the rest of the game due to a concussion.
"Concussions are very concerning, but all the stuff that you were really worried about, he was cleared," Shanahan said. "So, he remembers it all. Just the concussion, they'll keep him overnight for that."