Coming off a career game against the Baltimore Ravens, Tagovailoa's involvement in Sunday's big AFC East match-up looked set to end early.
The Dolphins quarterback took a hit late in the first half from Bills linebacker Matt Milano, who was flagged for roughing the passer.
Tagovailoa quickly got to his feet but then stumbled back to the ground.
He left the game to be assessed by medical staff, with the team announcing a head injury that made him questionable to return.
Yet Tagovailoa did return – a decision that has reportedly prompted an investigation from the NFL Players Association.
According to the player himself, though, it was a back problem that led to his worrying wobble, explaining why he was able to play again despite appearing to hit his head against the ground.
"I got my legs caught under someone – they were trying to push back and it felt like I hyper-extended my back or something," Tagovailoa said. "It kind of hurt.
"I got up, and that's why I stumbled. My back locked up on me. But for the most part, I'm good. I passed whatever concussion protocol they had."
Indeed, Dolphins coach Mike McDaniel said Tagovailoa was already ailing from an earlier incident.
"He got bent back pretty severe on a quarterback sneak earlier," the coach said.
"When he hit his head on the ground, I assumed it was a head injury, but his legs got wobbly because his lower back was completely loose, as he described it."