Antonio Brown was not with the Raiders on Sunday and Oakland general manager Mike Mayock told the wide receiver to decide if he was "all in or all out".
Brown, 31, skipped practice because he continues to be unhappy about his ongoing dispute with the NFL over his helmet, Mayock revealed when he met with reporters.
"Here's the bottom line," Mayock said.
"He's upset about the helmet issue. We have supported that, we appreciate that. 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. We're hoping he's back soon."
The helmet Brown wore with the Pittsburgh Steelers is no longer on the NFL's approved list. He lost an arbitration appeal to use the old model, and reportedly threatened to retire if he could not use the helmet.
The Raiders acquired Brown from the Steelers in March in exchange for draft picks. He caught 74 touchdown passes and made seven Pro Bowls during his nine seasons with Pittsburgh.
"We've got 89 guys busting their tails," Mayock said.
"We’re really excited about where this franchise is going and we hope A.B. is going to be a big part of it, starting week one against Denver. End of story."
Mayock declined to take questions from the media on Sunday. Brown has also dealt with frostbitten feet, an injury caused by a cryotherapy equipment mishap, in training camp.
The Raiders have two preseason games remaining before they host the Denver Broncos on September 9.