Mathis initially passed the concussion protocol on Oct. 25 and Lions head athletic trainer Kevin Bastin said Mathis showed up the following day without any symptoms. On Oct. 29 in London, Mathis woke up with what Bastin said were “light headaches,” but at the time the Lions' medical staff did not think it was related to the initial hit Mathis took against the Vikings.
Mathis practiced Thursday and Friday in England and woke up Sunday morning with another headache – and was held out of the game against the Chiefs. He was listed on the injury report in Week 8 as having an “illness.” Bastin said at the time the team physician did not think the headaches were related to the hit he took against the Vikings.
When the Lions returned from London, Mathis was again sent to the team doctors and an independent neurologist. At that time, he was placed in concussion protocol and is listed on the injury report with a concussion.
“It was not determined until last week whenever he saw the independent doctor,” Bastin said Wednesday. “The independent doctor said let’s go ahead and put him into the concussion protocol.”
Mathis was in attendance at Lions practice Wednesday, but was not practicing. Bastin said he is in Stage 2 of the protocol, known as light exercise. He has three more stages – and another meeting with an independent neurologist – before he can be cleared to return to the field for Detroit.
The next steps for Mathis are a full cardio workout (Stage 3), a non-contact practice (Stage 4) and then a full practice (Stage 5).
“There’s still a lot of unknowns with how [concussions] happen and in my history, we’ve had guys a couple weeks later come up with symptoms,” Bastin said. “And you always go back to the possibility that it could be from a prior blow.”
Mathis told ESPN.com earlier this season he had not been officially diagnosed with a concussion from football-related activities during his NFL career.