Houston Texans head coach Bill O'Brien told reporters Monday he "never would have allowed (Tom Savage) back in the game" had he seen the video of the quarterback's hands appearing to shake involuntarily.

O'Brien also said he asked Houston's medical staff to examine Savage a second time after they initially cleared him to return to Sunday's game against the San Francisco 49ers at NRG Stadium. Savage sustained a concussion in the second quarter and was slow to his feet after he was drilled by 49ers defensive end Elvis Dumervil.

Savage entered the sideline medical evaluation tent following the drive and returned to the field when the Texans regained possession. However, at the 2:32 mark of the second quarter, backup T.J. Yates replaced Savage behind center, with the latter seen on the sideline lobbying to return to the field yet again.

"I figured he got hit, didn't know he got hit, very difficult from where I'm standing to even see he got it. There's no video on the sideline," O'Brien said Monday. "With benefit of the video, I never would have allowed the player back in the game and I don't think (trainer) Geoff Kaplan would have let Tom back in the game."

O'Brien said after the first "quick check," he told Kaplan he thought Savage needed to be evaluated again.

"It wasn't anything that I particularly saw on the field. I just said, look, that was a quick check," O'Brien said Monday. "It was a three-and-out on that series. Let's continue to check him to make sure that the player, Tom Savage, is OK. They went, they checked him, they came to me, they were not satisfied with his answers to the questions that they were asking him, and they pulled him from the game."

NFL spokesperson Joe Lockhart told reporters during a Monday conference call that the league has initiated a joint investigation with the NFL Players Association into the handling of the issue involving Savage.

"That work started yesterday afternoon and continued into this morning, but I think we'll withhold further comments until we've had a chance to conduct the review," Lockhart said. "We believe very strongly that the protocol is an important part of our overall effort on protecting our players health and safety. But we do understand that it is our obligation to look at where the protocol may not have been followed, and just as importantly to see where the protocol can be improved. That's an ongoing effort."

Lockhart was asked if those on the sideline have access to the video that television viewers saw. He said spotters are able to send video to "relevant personnel on the field" and that the review will reveal what was seen and who saw it.

George Atallah, the assistant executive director of external affairs for the NFLPA, tweeted on Monday that, "we are initiating a full review of the Tom Savage concussion from yesterday's game."

O'Brien vehemently declared on Monday that he was "not passing the buck" for what occurred in the situation involving Savage, but that he had not seen the video given to where he was located on the field.

"At no point in time in my coaching career, in my 25 years of coaching, I've been at Brown University, I've been at Georgia Tech, I've been at Duke, I've been at the University of Maryland, I've been the head coach at Penn State and I've been the head coach here, at no point in time is there anything more important to me than the safety of our players," O'Brien said. "I love our players and I care about them and I cannot stand when players get injured. Again with benefit of seeing the video that people are seeing, I would have never put him back in the game."

O'Brien said that Yates is expected to start for the Texans (4-9) on Sunday when they visit the Jacksonville Jaguars (9-4) at EverBank Field. Yates was 14-of-26 passing for 175 yards and two touchdowns in relief of Savage on Sunday.