NAPA, Calif. -- Antonio Brown left training camp again Sunday, and though Mike Mayock said it was over the receiver's anger from being denied use of his helmet, the Oakland Raiders' general manager also issued an ultimatum to Brown.

"You all know that AB is not here today, right?" Mayock told a group of beat reporters as practice began Sunday afternoon. "So, here's the bottom line: He's upset about the helmet issue. We have supported that, we appreciate that. But at this point, we've pretty much exhausted all avenues of relief.

"So, from our perspective, it's time for him to be all-in or all-out, OK? 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 AB's going to be a big part of it, starting Week 1 against Denver. End of story. No questions, OK? Just wanted you guys to know where we were. Fair?"

"Here's the bottom line -- he's upset about the helmet issue. We have supported that, we appreciate that. But at this point, we've pretty much exhausted all avenues of relief. So, from our perspective, it's time for him to be all-in, or all-out, OK? So, we're hoping he's back soon."

Brown's agent, Drew Rosenhaus, responded to Mayock's comments later on Sunday, taking issue with his assertion that all avenues over the helmet issue have been exhausted.

"There's no doubt it's still an ongoing process," Rosenhaus told South Florida's 7 Sports Extra. "We are trying to work with the team and the league and the union to come up with a solution. We haven't figured it out yet. To say that AB is upset about the decision to not let him wear his helmet is accurate, but we're still processing it and figuring it out. I wouldn't make too much about him not being there today, as much as we're still trying to come up with a solution that works for everyone."

It has been an eventful and somewhat exhausting first Raiders camp for Brown, acquired in a March trade for a third- and a fifth-round draft pick. Because after being a mainstay during the team's offseason program, Brown began camp on the non-football injury list because of frostbite on the soles of his feet after a cryotherapy mishap in France in early July.

He left camp for two weeks, seeking therapy for the feet, which included laser treatments.

Brown has also been upset with the league's 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.

He returned to Napa on Tuesday and traveled with the team to Arizona for Thursday night's exhibition and ran routes and caught passes in pregame warm-ups. The Raiders were excited about Brown's return, and after he was a full participant in Saturday morning's walk-through, the team anticipated him practicing fully as soon as Sunday.

"I'm not talking about it anymore," Raiders coach Jon Gruden said of Brown's helmet after the Arizona game. "It was a legal, certified helmet, you know? Somebody approved it, or he wouldn't have worn it."

Brown later responded critically to a Pro Football Talk report about his helmet issue with a tweet Saturday, calling out the NFL for "super prejudice."

In 24 days in Napa, Brown took a hot-air balloon ride at dawn on report day, participated in one pre-practice walk-through on July 28, was limited before leaving early on July 30, took part in pregame warm-ups in Arizona on Thursday and was a full participant in Saturday's morning walk-through.

The Raiders were supposed to break camp Monday but ended a day early.

Asked earlier how much Brown changes the offense when he's on the field, Raiders offensive coordinator Greg Olson said:

"Significantly. He's one of the top players in the game. Anytime you're able to have that kind of talent on the field, he's going to draw the attention of defensive coordinators and players. Just changes really dramatically when you have those type of players."