Miami Dolphins quarterback Tua Tagovailoa showed no initial sign of concussion and there was no violation of protocol in allowing him to play on against the Green Bay Packers, an official review has determined.
The NFL and NFL Players Association (NFLPA) issued a joint statement on Saturday after delving into the circumstances once it emerged Tagovailoa suffered a concussion in last Sunday's game. It was a concussion that was not detected until the next day.
Dolphins head coach Mike McDaniel told reporters on Wednesday that film from the Packers game had been reviewed, leading team officials to question Tagovailoa on how he felt after a particular hit, sending him to see the doctors after inconsistencies in the quarterback's behaviour caused concern.
Tagovailoa will sit out the game against the New England Patriots on New Year's Day, with Teddy Bridgewater set to start in his place.
Star quarterback Tagovailoa also missed two games in October after another concussion, where he was hospitalised during a 27-15 Week 4 loss to the Cincinnati Bengals after being whipped around and flung to the ground by the Bengals' Josh Tupou, causing his head to snap back onto the turf.
In that instance, the Dolphins were heavily criticised for having Tagovailoa on the field just four days after an incident in a 21-19 win over the Buffalo Bills, where he was pushed to the ground by linebacker Matt Milano, with his helmet slamming into the turf.
In a statement widely reported by US media on Saturday, the NFL and NFLPA said they had completed a review of the application of the concussion protocol in the Christmas Day game.
"The joint review determined the protocol was not triggered," the statement said. "The protocol is initiated when a player receives an impact to the head and exhibits or reports signs or symptoms suggestive of a concussion.
"The review established that symptoms of a concussion were neither exhibited nor reported until the following day at which time the team medical personnel appropriately evaluated and placed Mr Tagovailoa in the concussion protocol."
The Dolphins are 8-7 for the season following their 26-20 loss to the Packers, in which Tagovailoa threw three interceptions, and have now suffered four losses in a row.
McDaniel said this week that Tagovailoa's health holds more importance than the games that lie ahead.
"This is a private time for him to focus on his health. This is a human being. His health is the first and only priority," McDaniel said.