"He's all in, ready to go," Gruden said after the workout. "That's my understanding. Really happy to have him out here. He's a great player."
Gruden also said it appears Brown has put his frostbitten feet behind him ... saying he's under the impression AB is healthy and ready to go.
But, AB is still holding out hope he can switch back to his old helmet ... a source close to Brown confirmed with TMZ Sports on Monday that Brown has filed a new grievance with the league to try to get his old helmet cleared for at least the 2019 season.
Unclear when an independent arbitrator is set to hear Brown's case vs. the league, but NFL Network's Ian Rapoport reported it's supposed to be "expedited."
The Raiders kick off the season on Sept. 9 ... who's ready?!?!