Oakland Raiders wide receiver Antonio Brown lost his grievance against the NFL, a person familiar with the case said. Brown had asked to be allowed to wear a helmet not approved by the league.

The arbitrator ruled in the NFL’s favor Monday after conducting a hearing Friday, the person said. Barring an appeal to federal court, Brown must wear an approved helmet or remain on the sideline.

Brown suggested in a social media post that he intends to rejoin the Raiders. He reportedly had previously told the team that he would not play football again if not allowed to wear his preferred helmet.

“While I disagree with the arbitrator’s decision, I’m working on getting back to full health and looking forward to rejoining my teammates on the field,” he wrote on Instagram. “I’m excited about this season [and] appreciate all the concerns about my feet!”

Brown had been seeking to wear a helmet model that was discontinued by the manufacturer and was not certified by the national governing body, because it was more than 10 years old, according to a person familiar with the case. Brown was one of 32 NFL players who wore non-approved helmets last season and were told they would not be able to wear them this year under a program jointly administered by the league and the NFL Players Association.

Brown has not been practicing recently, because of injuries to his feet reportedly caused or worsened when he wore improper footwear during a cryotherapy treatment. The Raiders obtained the seven-time Pro Bowl selection in a trade with the Pittsburgh Steelers in March.