Brown lost an earlier grievance against the NFL that sought an exception to wear his Schutt Air Advantage, a helmet he has worn throughout his career. Brown then filed a second grievance Monday night, asking for a one-year grace period before needing to change helmets.
A number of players, including New England Patriots quarterback Tom Brady, were given a one-year grace period last season, but the NFL and NFL Players Association eliminated the grace period after last season.
Brown left the team twice in training camp in Napa, California -- the first time for two weeks to ostensibly seek treatment for his frostbitten feet; the second time on Sunday, skipping out on practice in anger over the league denying his helmet.
It prompted an "all-in or all-out" ultimatum from general manager Mike Mayock on Sunday.
Brown's agent, Drew Rosenhaus, told ESPN Radio's Golic & Wingo on Wednesday that his client will play this season, even if this second grievance is denied.
"There's never been the possibility that Antonio would let this prevent him from doing what he loves to do and fulfilling his destiny as one of the great receivers of all time," he said. "He is determined to play this year and what we're trying to do is get him in the safest equipment possible."
Brown, wearing a certified helmet, participated in practice Tuesday.
"He's all-in and ready to go," Raiders coach Jon Gruden said.
ESPN's Paul Gutierrez and Kevin Seifert contributed to this report.