Source: NFLPA to review handling of WR DeVante Parker's injury 1:44 PM ET ESPN The NFL Players Association has initiated an inquiry into why Monday night's game wasn't stopped when New England Patriots wide receiver DeVante Parker showed concussion symptoms, a source told ESPN's Dan Graziano on Tuesday. Parker was wobbly getting up after a hit in the first half, and teammate Nelson Agholor had to signal to the officials to stop the game and remove Parker before the next play. Earlier this season, the NFLPA initiated a review after Miami Dolphins quarterback Tua Tagovailoa was allowed to return to a Sept. 25 game despite hitting his head on the ground and stumbling while attempting to return to the huddle. Tagovailoa told both the Dolphins' team physician and the unaffiliated neurotrauma consultant that an ankle and back injuries caused him to stumble. He was cleared to play in a game four days later and again hit his head on the ground, suffering a concussion and was briefly hospitalized. Editor's Picks Pats lose Stevenson, Parker to injuries on MNF 11h Mike Reiss NFL, NFLPA agree to amend concussion protocol 66d Marcel Louis-Jacques 1 Related Following that review, the unaffiliated neurotrauma consultant for the Sept. 25 game was fired and the NFL and the players' union implemented an amendment to the concussion protocol. Both parties agreed to amend the protocol by adding ataxia to the list of "no-go" symptoms. "'Ataxia' is defined as abnormality of balance/stability, motor coordination or dysfunctional speech caused by a neurological issue," their joint statement read. "In other words, if a player is diagnosed with 'ataxia' by any club or neutral physician involved in the application of the Concussion Protocol, he will be prohibited from returning to the game, and will receive the follow-up care required by the Protocol." Parker sustained his head injury on a 10-yard catch at the 4:19 mark of the first quarter following a hit and tackle by Arizona Cardinals defensive back Antonio Hamilton over the middle. Parker entered Monday with 23 receptions for 436 yards and one touchdown on the season. He had played 65% of the team's offensive snaps. ESPN's Mike Reiss contributed to this report.