Tagovailoa failed to clear the NFL's concussion protocol. Tagovailoa missed the past two games after suffering a concussion during Miami's game against the Green Bay Packers in Week 16.
"Tua has not been cleared by doctors to resume football activities with his teammates," McDaniel told reporters Wednesday. "Because of that and because of the time he's missed, I can rule him out for Sunday."
McDaniel wouldn't say if Tagovailoa would travel with the team to Buffalo but added that the team is preparing to start rookie quarterback Skylar Thompson, but that veteran Teddy Bridgewater is working to get ready to play Sunday after he suffered a broken thumb in Week 17.
It's a troubling development for Tagovailoa and the Dolphins' once-promising season. Tagovailoa missed two games earlier this season with a different concussion and his history with head injuries this season alone has raised a bevy of concerns and questions about the league's handling of concussions.
"He was an incredible part of the entire season," McDaniel said of Tagovailoa. "I think eight of our wins were as a result of him playing quarterback amongst the team. That did not come because it was gifted. That was a lot of work and preparation. So it's very frustrating, much as a lot of things in life and football are. But it's very frustrating for him not to go through everything with his teammates. It was a huge goal of his help get this team to the playoffs and he wants to play in the playoffs."
Tagovailoa's appeared to hurt his head against the Bills in Week 3 when he stumbled after taking a big hit. He left the game but returned after halftime with what the team called a back injury. Tagovailoa suffered an official concussion five days later in Week 4 against the Cincinnati Bengals during which he had to be taken off the field in an ambulance.
Though he returned in Week 7 and played the next nine games, Tagovailoa reentered the concussion protocol after the Dolphins' loss to the Packers after he spoke with team doctors. Miami ruled him out for the team's final two games of the regular season. Miami returned to Bridgewater in Week 17, only to lose him to a broken finger in the third quarter. Thompson played the rest of that game before starting and beating the New York Jets in Week 18 to secure Miami's playoff berth.
No Tagovailoa is bad news for the Dolphins. Miami averaged 16.5 points in the four games he didn't play, compared with the 25.5 points the team averaged when Tagovailoa played. The Dolphins will also be without starting running back Raheem Mostert, who suffered a broken thumb in Week 18.