Antonio Brown's agent, Drew Rosenhaus, is confident that a solution will be found on Brown's helmet issue and expects him to play for the Raiders in Week 1. (1:36)

Agent Drew Rosenhaus said Monday that Antonio Brown's helmet concerns are safety-related and that the wide receiver is "all-in" with the Oakland Raiders.

Rosenhaus appeared on ESPN's Get Up! after Raiders general manager Mike Mayock said Sunday that Brown had left camp again over the helmet issue and it was "time for him to be all-in or all-out."

Rosenhaus disputed that Brown had left camp, saying that he just wasn't at practice Sunday and is still in the Napa Valley. He said he believed Brown would be back with the Raiders "soon" and that he and Brown were testing two additional helmets in an attempt to solve the issue.

Making good on his agent's words, Brown rejoined the Raiders at their facility Monday morning and was in attendance at the last team meeting before they broke training camp, a source told ESPN's Adam Schefter. The team returns to the home facility in Alameda and practices on Tuesday before departing for Winnipeg for Thursday night's exhibition against the Green Bay Packers.

Brown has been upset that the league is not allowing him to wear his Schutt Air Advantage helmet, the only helmet he has worn in his NFL career, because it is older than 10 years and, thus, no longer certified. A grievance he filed against the league to wear his old helmet was denied last week.

"He wore this helmet in Pee Wee football, high school football, college at Central Michigan and his entire nine-year career," Rosenhaus said. "People keep saying to me there's 2,000 players that are wearing approved helmets. But there are very few, if any, that have worn the same helmet their entire nine-year career.

"He's a wide receiver, he gets hit across the middle, people are trying to take his head off. He's a big target -- you talked about how many catches he's had over the last six years, for example. 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. ... 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. It is a major issue for him."

Rosenhaus said he and Brown "admire the fact that the NFL and the NFLPA are trying to make changes for player safety, but this has worked for Antonio. He feels very safe in this helmet and we want to make sure we do everything we can to keep him safe."

Rosenhaus also proposed that perhaps a helmet could be "custom made" for Brown if the additional helmets he tries out don't solve the problem. He said he has been working with the Raiders, the NFL and the NFLPA on Brown's helmet issue since March and that he called Mayock several times on Sunday.

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"We've been talking to helmet companies, trying to get this straightened out, trying to find a helmet that will work, trying to get his helmet approved, trying different helmets," Rosenhaus said. "Antonio's probably worn 15 different helmets to try to find something similar to what he currently has. We've been unable to do that, but we're going to continue to work.

"I called Mike late last night and said, 'Let's get every available helmet that's approved and get every one of them out. Let's find a solution.' We are working with the team to get this done. I don't expect this to be a long-term issue. I'm working with Antonio, I'm working with the team, I'm working with the league, the union, everybody that you can think of to get this hammered out."

Rosenhaus said he was confident that a solution can be found and that he expects Brown to be on the field when the Raiders play the Denver Broncos in Week 1.

"I don't see any reason why he wouldn't be. I believe we're going to get this worked out in time for him to be there," he said.

After he was traded to the Raiders in March from the Pittsburgh Steelers, Brown signed a three-year deal worth up to $54.125 million, with $30.125 million guaranteed. He previously had three years and $38.9 million left on his contract with the Steelers, with none of the money guaranteed.

ESPN's Paul Gutierrez contributed to this report.