Commissioner Roger Goodell expanded on his decision in the following letter to Peterson:
"The timing of your potential reinstatement will be based on the results of the counseling and treatment program set forth in this decision. Under this two-step approach, the precise length of the suspension will depend on your actions. 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. 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."
The NFLPA filed a non-injury grievance last week on Peterson's behalf. On Tuesday, arbitrator Shyam Das ruled in favor of the league, NFL Media's Ian Rapoport and Albert Breer reported per league and union sources. This means Peterson remains on the Commissioner's Exempt List while he awaits the result of a planned appeal. The running back will continue to be paid while he's on the list.
Peterson pleaded no contest to misdemeanor reckless assault earlier this month on what the league called "an incident of abusive discipline" toward his 4-year-old son.
Peterson was most recently coming off a Monday hearing on his status on the Exempt list, which opened the door for Tuesday's decision by the NFL. Barring a successful appeal, they will not get that chance until training camp in 2015.
Peterson will lose $4.2 million during his suspension over the next six games and isn't owed any more guaranteed money, Rapoport added.
The NFLPA quickly released a statement about appealing the decision, calling the suspension "another example of the credibility gap that exists between the agreements they make and the actions they take." The union is also demanding that a neutral arbitrator oversee the process.
"We call on the NFL Management Council to show our players and our sponsors leadership by committing to collective bargaining so a fair personal conduct policy can be implemented as quickly as possible," the statement read.