Miami Dolphins quarterback Tua Tagovailoa will have an MRI after sustaining neck and head injuries in Thursday night's loss to the Cincinnati Bengals.
CBS Sports reported Tagovailoa travelled back to Miami with his team while wearing a neck brace. Initial scans performed at a Cincinnati hospital were negative.
The Dolphins said he sustained a concussion, and NFL Network reported that Tagovailoa has entered the league's concussion protocol.
Tagovailoa was sacked by Cincinnati's Josh Tupou and swung to the ground violently with just under six remaining in the first half.
His head and upper back hit the turf hard and his fingers displayed a distressing fencing response after the incident.
Tagovailoa was down on the field for approximately 10 minutes before being taken off the field and taken by ambulance to the University of Cincinnati Medical Center.
According to the Dolphins, Tagovailoa remained conscious throughout the night and had full movement in his extremities.
The injury came four days after Tagovailoa briefly left Sunday's game against the Buffalo Bills in what looked like a disorientated state and returned after passing the concussion protocol.
Earlier in the week, the NFL Players Association indicated it would conduct an investigation into the quarterback being allowed to return to the field.
"Player health and safety is at the core of the union's mission," the union tweeted Thursday night. "Our concern tonight is for Tua and we hope for a full and speedy recovery. Our investigation into the potential protocol violation is ongoing."
The Dolphins lost the game 27-15 for their first defeat of the season.
Joe Burrow passed for 287 yards and two touchdowns and Evan McPherson kicked two fourth-quarter field goals.
Tee Higgins caught seven passes for 124 yards and one touchdown for the Bengals. Vonn Bell intercepted two passes, Joe Mixon rushed for a score and Hayden Hurst caught a touchdown pass.
Teddy Bridgewater replaced Tagovailoa in the second quarter and completed 14 of 23 passes for 193 yards, one touchdown and one interception for Miami.
Tyreek Hill caught 10 passes for 160 yards for the Dolphins, whose loss leaves the Philadelphia Eagles as the NFL's lone unbeaten team.