ALAMEDA, Calif. — Star receiver Antonio Brown returned to practice with the Oakland Raiders on Monday, a day after being given an ultimatum by general manager Mike Mayock to be “all in or all out.”

Brown took part in meetings in Napa before the team broke camp, a person familiar with the situation said on condition of anonymity because the team didn’t release details.

Brown didn’t attend practice Sunday as he works to find a helmet that he’s comfortable using and that meets safety standards set by the NFL and NFLPA. Brown lost a grievance last week seeking to use the Schutt Air Advantage helmet he has used throughout his career because it was too old to be certified as safe.

He had hoped to find a newer version of his preferred helmet that could be approved but the one he submitted failed a safety test conducted by the league and union, a second person said on condition of anonymity because test results weren’t released.

Agent Drew Rosenhaus told ESPN earlier Monday that he expects Brown to be back practicing soon and that they are looking into “all options right now to resolve the helmet issue.” The Raiders’ next practice will be Tuesday.

”Antonio is very genuine,” Rosenhaus said. “He wants to be there. He wants to be a part of the team. He wants to practice. But he’d also like to do it with the helmet that he’s worn his entire life. He wore this helmet in pee-wee football, high school football, in college at Central Michigan. And he also wore this helmet his nine-year (NFL) career.

”This is his life. He’s risking everything. He’s got a family. He’s had a concussion before. This helmet has kept him safe. He’s had brutal hits. And we’re just trying to find a way to work it out. We’ve worked very closely with the Raiders, we’ve worked very closely with the NFL. But I hope people can appreciate this is not a simple issue. The helmet is the most important piece of equipment and he’s had the same one every single snap he’s played in his football career. This is a major issue for him.”

Brown has yet to take part in a full practice all training camp for the Raiders, missing time because of frost bite on his feet suffered in a cryotherapy accident in France and now over the helmet issue.

That led to Mayock’s public frustration Sunday when he said the Raiders had supported their star player but had “exhausted all avenues of relief.”

”So from our perspective, it’s time for him to be all in or all out,” Mayock said. “So we’re hoping he’s back soon. We’ve got 89 guys busting their tails. We are really excited about where this franchise is going and we hope A.B. is going to be a big part of it starting Week 1 against Denver.”

Brown had 686 catches and 9,145 yards receiving the past six seasons in Pittsburgh, the best marks ever for a receiver in a six-year span. But he still wore out his welcome with the Steelers after leaving the team before a crucial Week 17 game last season and was able to be acquired by Oakland in March for the small price of third- and fifth-round draft picks.

The drama that surrounded Brown in Pittsburgh didn’t stop upon his arrival with the Raiders even though he was given a hefty raise with a three-year contract worth $50.125 million.

Brown arrived at camp with frost-bitten feet, sending him to the non-football injury list. He was activated on July 28 and participated in parts of two practices before leaving the team to get treatment on his feet and to deal with the grievance with the NFL. Brown returned to the Raiders on Aug. 13 but still hasn’t participated in a full practice all of training camp.