Oakland Raiders wide receiver Antonio Brown has lost his second grievance hearing with the NFL regarding the use of his old helmet, but he is moving forward with a deal for an approved helmet in the near future, sources confirmed to ESPN on Sunday.

Brown lost an earlier grievance against the NFL that sought an exception that would allow him to wear his outdated Schutt Air Advantage helmet, which he has worn throughout his career. Brown then filed a second grievance Monday, asking for a one-year grace period before needing to change helmets.

The NFL and NFL Players Association eliminated the grace period after last season.

The second hearing, which took place Friday, was heard by the same independent arbitrator that presided over the first hearing, sources told ESPN. The NFLPA submitted an affidavit in support of the league's position to not allow Brown to wear the older helmet, sources told ESPN.

ProFootballTalk first reported that Brown had lost the second hearing.

Helmet testing and regulations are administered jointly by the league and the NFLPA.

Brown, who showed up for training camp on July 26 with frostbite on the bottom of both feet due to a cryotherapy mishap in France, left the team for two weeks to seek treatment as well as in protest of the league's banning his 10-year-old helmet. Later, he skipped camp a day after his first grievance was denied.

Agent Drew Rosenhaus told ESPN's Golic and Wingo after the first hearing that Brown would play with an approved helmet going forward and not retire.

Brown, who participated in practice Tuesday wearing a certified helmet, took the practice field Sunday wearing what appeared to be an older helmet.

A look at Antonio Brown's helmet before #Raiders practice... pic.twitter.com/5zLYY0tKra

— Paul Gutierrez (@PGutierrezESPN) August 25, 2019

Brown went with the team to Winnipeg, Manitoba, last week and, for the second consecutive exhibition, ran routes and caught passes from quarterback Derek Carr in pregame warm-ups.

The Raiders on Sunday placed running back Doug Martin on injured reserve. In other roster moves, the team released long-snapper Andrew DePaola and signed defensive tackle Corey Liuget and linebacker Bryson Allen-Williams.

The moves essentially mean rookie Josh Jacobs will be the Raiders' feature running back and Trent Sieg will be the team's long-snapper.

ESPN's Adam Schefter and Dan Graziano contributed to this report.