Dallas Cowboys running back Ezekiel Elliott's six-game suspension was upheld on Tuesday.
Elliott was handed the ban last month for violating the NFL's player conduct policy.
The ruling followed a year-long NFL investigation into domestic violence accusations made against Elliott by his ex-girlfriend, Tiffany Thompson. Elliott denies the allegations and was never charged.
Arbitrator Harold Henderson announced his decision on Tuesday, but Elliott could see the field beyond week one against the New York Giants pending additional legal action.
"We are extremely disappointed with Mr. Henderson's inability to navigate through league politics, and follow the evidence, and most importantly, his conscious," Elliott's legal team said in a release.
"The evidence that Mr. Elliott and his team presented on appeal clearly demonstrated that Mr. Elliott was the victim of a conspiracy orchestrated by the National Football League and its officers to keep exonerating evidence from the decision-makers, including the advisors and Roger Goodell.
"The only just decision was to overturn the suspension in its entirety. Mr. Elliott is looking forward to having his day in federal court where the playing field will be level and the NFL will have to answer for its unfair and unjust practices."
Elliott's lawyers accused the NFL of a league-orchestrated conspiracy in a temporary restraining-order motion last week. Should a judge rule in his favour, Elliott could delay the six-game suspension and play all season. If not, Elliott would sit out weeks two through seven and return to the field on November 5 against the Kansas City Chiefs. A ruling on the restraining order is expected Thursday or Friday.