Brown had a two-hour conference call with an independent arbitrator on Friday, sources said, to argue why he should be allowed to wear his 10-year-old helmet. He is thought to have been using the same helmet his whole career.
The arbitrator for the grievance call was joined by league officials, player representatives and NFLPA representatives in Philadelphia, a source told ESPN. A decision could come as early as next week, sources said.
Brown wants to wear the helmet he prefers, not one of the newer-model helmets that league rules mandate, league sources said. Brown believes the new certified helmet protrudes out and interferes with his vision as he tries to catch the football.
The Raiders have been sending Brown other approved helmets to wear, but at this time, he is not interested in wearing any of them.
Brown appeared to refer to an internal debate about walking away from football by posting Friday an Instagram caption paraphrasing the 2002 movie "Paid In Full."
League sources also told ESPN that Brown's recent absence from Raiders training camp has more to do with his helmet than with his feet. He suffered extreme frostbite on his feet as a result of not wearing appropriate footwear when he entered a cryotherapy chamber last month in France, a source told ESPN.
The helmet that Brown is comfortable in and wore throughout his nine seasons with the Pittsburgh Steelers -- believed to be the Schutt Air Advantage helmet, which the company has discontinued making -- is no longer certified by the National Operating Committee for Standards and Athletic Equipment.
The NFL has a policy of not allowing players to wear helmets that are not certified by NOCSAE, and the committee's rule has been that no helmets older than 10 years can be worn.
Kornheiser on AB's helmet situation: 'This can't be good'
Tony Kornheiser and Frank Isola share their opinions on Antonio Brown refusing to play football for the Raiders without his old helmet.
It's the latest complication in what has become a complicated summer for Brown, from his head to his feet.
The foot injury has limited his practice time, and he has not been in camp recently as he meets with specialists. Other league sources, however, told ESPN that the helmet issue has been an ongoing battle since the start of training camp.
The NFL and NFL Players Association want players to wear helmets designed in the most effective manner to safeguard against potential head injuries.
The Raiders are "aware and supportive of Antonio Brown but [have] no further comment."
During the offseason, the NFL and NFLPA added 11 helmets to their joint list of approved equipment for this season while eliminating a grace period for other models that have fallen short in laboratory testing. By the end of last season, the NFL said 32 players were wearing helmets that now are banned. Brown was one, and Patriots quarterback Tom Brady -- who has openly complained about the rule -- was another.
Though the league and NFLPA have tested helmets since 2015, last year marked the first time they banned certain models. This season, the league is enforcing the rule and trying to make no exceptions, even saying that any player wearing a banned helmet will be subject to discipline.