An arbitrator on Friday upheld the NFL's suspension of Adrian Peterson, likely ending any chance Peterson had to return to the playing field this year.

The only path left for the Vikings star is a legal appeal, and the team's season will end in just over two weeks.

Harold Henderson, former NFL executive vice president for labor relations and the hearing officer appointed by NFL Commissioner Roger Goodell, ruled that Peterson must remain away from the league and all team activities until at least April 15. Peterson will be eligible to return then if he fulfills requirements set by Goodell last month, when he suspended Peterson for the rest of the regular season.

The league's 2012 Most Valuable Player will also forfeit six game checks from the 2014 season, costing him $4.1 million from his $11.75 million salary.

In an interview with ESPN, Peterson compared his case to that of Ray Rice, the former Baltimore running back, whose indefinite suspension for a domestic assault case was overturned by an independent arbitrator Dec. 1.

"I've been made an example out of," Peterson told ESPN. "It kind of baffles me how — I have nothing but love for Ray Rice, I'm happy he has the chance to play. But it's like, how did Ray Rice get reinstated before me, a team has a chance to pick him up, but I don't have the opportunity to come back until April? When has that happened in any other case in the NFL, ever?"

Adrian Peterson

The NFL Players Association, which asked that Henderson step aside as arbitrator before the hearing because of his ties to the league, said it was considering "immediate legal remedies."

The Vikings declined to comment on the news.

Peterson, 29, was suspended by Goodell on Nov. 18 following his no contest plea in Houston to a misdemeanor charge of reckless assault. He had been indicted by a Texas grand jury in September on a felony charge after injuring his 4-year-old son by whipping him with a "switch," a tree branch. Peterson, placed on the Commissioner's Exempt List until his court case was settled, appealed the suspension based on his belief that an NFL official had promised him he would get credit for "time served," plus a two-game suspension.

"I conclude that the player has not demonstrated that the process and procedures surrounding his discipline were not fair and consistent," Henderson wrote in an eight-page letter explaining his decision. "He was afforded all the protections and rights to which he is entitled, and I find no basis to vacate or reduce the discipline."

Henderson said that the facts in Peterson's appeal were uncontested. "The player entered a plea which effectively admitted guilt to a criminal charge of child abuse, after inflicting serious injuries to his four-year-old son in the course of administering discipline," he wrote. Henderson added that Peterson's conduct was "egregious and aggravated" and merited "substantial discipline" under the league's personal conduct policy.

Henderson also wrote that Peterson's public comments regarding his charges "do not reflect remorse or appreciation for the seriousness of his actions and their impact on his family, community, fans and the NFL."

Henderson did indicate, however, that at the close of his appeal hearing, Peterson said he has learned from his mistake, regrets that it happened and said it will never happen again.

Peterson's contract with the Vikings runs through 2017. The $36 million in guaranteed money in the deal has already been paid, and his salary next season would be $12.75 million. The team could rework the contract to save money, or cut him with no financial obligation.

Peterson played in a Week 1 victory at St. Louis, then was deactivated for the team's second game following his Sept. 12 grand jury indictment. After a very brief reinstatement protested publicly by some of the league's and team's corporate sponsors, he was placed on the exempt list Sept. 16.

In his letter following the suspension, Goodell wrote that Peterson violated the league's personal conduct policy "in an incident of abusive discipline." He called what Peterson did to his son "emotional and psychological trauma" that came in the form of "criminal physical abuse at the hands of his father."

"We are prepared to put in place a program that can help you to succeed, but no program can succeed without your genuine and continuing engagement," Goodell wrote. "You must commit yourself to your counseling and rehabilitative effort, properly care for your children, and have no further violations of law or league policy."

In the letter, Goodell said another requirement for reinstatement was for Peterson to meet with a league-appointed psychiatrist to design a mandatory program of counseling, therapy and possible community service.

The players' union argued that Peterson was being retroactively punished by the league's new "enhanced discipline" personal conduct policy as it related to domestic violence. That policy was introduced in August — three months after Peterson whipped his son.

The players' union "expected this outcome, given the hearing officer's relationship and financial ties to the NFL,'' the group said in a statement. "The decision itself ignores the facts, the evidence and the collective bargaining agreement."

But Henderson concluded that Goodell had the same authority to punish Peterson under the previous policy.

"While the discipline assessed is indeed greater than in most prior cases, this is arguably one of the most egregious cases of domestic violence in this Commissioner's tenure," Henderson added.

Peterson's salary next season would be the highest in the NFL for his position. And given his suspension for the rest of the 2014 season, it's possible that one of the most productive running backs in NFL history has played his last game as a Viking.