Getty Images

Though the exact language is still being negotiated, the NFL and NFL Players Association are nearing a change to the concussion protocol that would prevent a player from re-entering the game after a head-hit and stumble like Dolphins quarterback Tua Tagovailoa suffered in Week 3 against Buffalo.

Sources tell CBS Sports the main change will be focused on ataxia. According to the Mayo Clinic, ataxia "describes poor muscle control that causes clumsy voluntary movements. It may cause difficulty with walking and balance, hand coordination, speech and swallowing, and eye movements."

Tagovailoa exhibited gross motor instability in the moments after his head hit the turf against Buffalo. That instability is considered a "no-go" in the concussion protocol unless the instability is determined to be not neurologically caused. In Tagovailoa's case, a back injury was what doctors seemed to determine as the cause of the instability and he was allowed back in the game.

Under the proposed protocol, Tagovailoa would not be allowed to re-enter the game. Essentially if there's some sort of visible head trauma — a fall or a helmet-to-helmet hit — that is followed by some sort of gross motor instability, that player would not be allowed back in the game.

The hard line on gross motor instability and reintroduction to the game has been a difficult one for the league and union to take. A player can stumble due to any number of legitimate medical issues like a back or ankle injury. Just because a player exhibits instability isn't reason enough to remove him from the remainder of the game.

Sources indicate the language is still being negotiated between the league and union. There was optimism on both sides that protocols could be in place by Thursday night's game between Indianapolis and Denver. By Friday evening with no agreement in place, the union issued a statement that placed some public pressure on the league.

"Our union has agreed to change the concussion protocols to protect players from returning to play in the case of any similar incident to what we saw on September 25," the NFLPA statement read. "We would like these changes to go into effect before this weekend's games to immediately protect the players and hope the NFL accepts the change before then as well."

The NFL responded with a statement of its own shortly after on Friday night.

"As we have discussed with the NFLPA, we agree that changes to the joint NFL-NFLPA protocols are necessary to further enhance player safety," the league statement read. "We have already spoken to members of the NFL Head, Neck and Spine Committee and the leadership of the Unaffiliated Neurotrauma Consultants and Independent Certified Athletic Trainers who serve as spotters to discuss these likely changes."

The NFLPA previously exercised its right to fire the unaffiliated neurotrauma consultant who examined Tagovailoa on Sept. 25. The union has stated that the independent doctor made "several mistakes" in its view. The league has yet to comment on that.

The review into the handling of Tagovailoa's concussion check during the game remains ongoing. There was similar optimism Thursday the review would conclude and findings publicly released by the end of the week, but that has yet to occur.