After losing a previous grievance in which he lobbied for permission to wear his Schutt Air Advantage helmet during the 2019 season, Brown filed another grievance this week.
The NFL's new helmet rule states that players must wear an approved helmet produced within the past 10 years. Brown thought he had found a version of his preferred helmet that fit the parameters, but the NFL said it was not usable.
Although the NFL and NFL Players Association eliminated the one-year grace period for helmets at the conclusion of the 2018 season, Brown believes he is owed a grace period since the replacement helmet he found was only recently banned.
Brown returned to practice this week wearing a certified helmet, and Raiders head coach Jon Gruden told reporters the seven-time Pro Bowler was focused on football: "He's all-in and ready to go. That's my understanding. Really happy to have him out here. He's a great player."
In addition to the helmet issue, Brown is recovering from burns to his feet suffered when he didn't use proper footwear in a cryotherapy chamber.
Brown has yet to appear in a preseason game for the Raiders, and it is unclear if he will see any game action prior to the team's regular-season opener against the Denver Broncos on Sept. 9.
Oakland acquired Brown in an offseason trade with the Pittsburgh Steelers, and he is expected to be the No. 1 target for quarterback Derek Carr in the passing game.