Brown suffered extreme frostbite in July because he didn't wear proper footwear while using a cryotherapy chamber in France, but while that was viewed as the reason he missed the early stages of training camp, it turned out the helmet issue was actually the driving factor in his absence, per ESPN's Adam Schefter.
The 31-year-old Miami native went as far as informing the Raiders he would retire from the NFL unless his longtime helmet, the Schutt Air Advantage, was granted clearance, according to Schefter.
Brown even used social media in an effort to find a similar model that would meet regulations:
Tom Pelissero of the NFL Network reported the league and its players association wouldn't clear the seven-time Pro Bowl selection's old helmet after it failed testing.
Brown's decision to file a second grievance came after Oakland general manager Mike Mayock released a statement about the team wanting to know whether the receiver was "all-in or all-out":
The Raiders acquired the Central Michigan product from the Pittsburgh Steelers in March for third- and fifth-round picks in the 2019 NFL draft.
Brown recorded 837 catches for 11,207 yards and 74 touchdowns in 130 regular-season games across nine seasons with the Steelers.
The second failed grievance gives the superstar wideout a limited number of options with the regular season looming. He must now decide whether he's willing to walk away from football, and his three-year, $50.1 million contract, because of the helmet issue.
For now, Oakland must prepare for the possibility Brown sits out, which would significantly decrease the team's offensive upside. Tyrell Williams would take over as the top target for quarterback Derek Carr, while rookie running back Josh Jacobs would need to make a massive instant impact.