The NFL is checking whether concussion protocol was properly followed Sunday when Houston Texans quarterback Tom Savage was allowed to briefly return to action after a hard hit in the end zone that left him dazed and with his hands quivering.

Texans coach Bill O'Brien said Monday that he didn't see the video of Savage shaking and never would have allowed him back in the game if he'd been able to see what the TV cameras showed.

League spokesman Joe Lockhart said the NFL and the players' association "together will conduct a thorough review of the incident focused on whether the protocol was properly followed, but we're also continuing looking at the protocol to look for ways to improve and strengthen it."

Lockhart said the discovery during this investigation of any possible improvements to the concussion protocol will be quickly implemented in co-ordination with the players union.

NFL Players Association spokesman George Atallah tweeted , "we are initiating a full review of the Tom Savage concussion from yesterday's game."

The NFL's concussion protocol came under heavy criticism after it failed Savage on Sunday in Houston's 26-16 loss to the 49ers. Only after Savage briefly returned to the game did the medical crew determine the quarterback did, indeed, have a concussion and remove him from participating.

"We are going to wait until we've had a chance to co-ordinate with the NFLPA and talk to all the people involved in the incident, everyone from the referees to the spotters to the UNCs (unaffiliated neurotrauma consultants) to the team physicians, head coach, player — whoever is relevant for this discussion before we reach any conclusions," Lockhart said.

Lockhart wouldn't speculate whether any officials saw the video of Savage's hit before clearing him to return to action. He said spotters do have the ability to send video to "relevant personnel on the field."

"That is a question that we will look at in this review of the incident," Lockhart said.

Lockhart also said he expects results "to be announced in the next day or two" of an investigation whether concussion protocol was properly followed involving Russell Wilson earlier this season.

Savage was hit by 49ers defensive end Elvis Dumervil while throwing an incomplete pass on third down in the second quarter in Houston. His helmet slammed into the ground and Savage appeared to have trouble getting up. He seemed dazed, his hands visibly quivering.

Referee John Hussey sent him to the sideline to get checked out. The NFL requires two trained spotters in the press box, a team doctor and an unaffiliated neurotrauma consultant on the sideline to help diagnose concussions.

After being checked out in the medical tent for less than three minutes, Savage returned to the game for a series and threw two incomplete passes.

O'Brien said Monday he told the team's athletic trainer, Geoff Kaplan, that he thought Savage needed to be further evaluated because it had been such a "quick check" initially.

"They were not satisfied with his answers to the questions that they were asking him and they pulled him from the game," O'Brien said.

Savage appeared to be trying to get back into the game a second time before he was stopped by an assistant coach from returning the field and was escorted by the trainer to the locker room just before halftime.

O'Brien noted Monday he didn't have access to the video and had no idea Savage had even been hit on the play.

"I'm on the 50-yard line calling the play" in which the 49ers blitzed six players, O'Brien said. "I figured that he got hit, really didn't know that he got hit, there's 12 bodies around him. Very, very difficult from the 50-yard line where I'm standing to see if he even got hit.

"With benefit of seeing video, obviously from my standpoint, the care for the player, I would have never let that player back in the game," he said. "And I don't believe that (team athletic trainer) Geoff Kaplan would have allowed that player back in the game. I do not have benefit of the video. I did not see anything."

O'Brien said he expects T.J. Yates, who threw two touchdown passes in relief of Savage on Sunday, to start next weekend when the Texans (4-9) visit the Jaguars (9-4).

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