The NFL Players Association filed an "expedited, non-injury grievance" against the NFL on Monday in an attempt to get Peterson reinstated immediately, according to Brad Biggs of the Chicago Tribune.
The NFL did not reinstate Peterson by the 5:00 p.m. Monday deadline the NFLPA had requested to the league, prompting the union to file the grievance.
Sports Illustrated's Andrew Brandt reports the arbitrator who will make the ruling, Shyam Das, was fired as an arbitrator by Major League Baseball after overturning Milwaukee Brewers outfielder Ryan Braun's performance-enhancing drugs suspension in 2012.
Peterson will miss the Vikings' Week 10 game against the Chicago Bears, but will have a ruling before the Vikings play the Green Bay Packers at home on Nov. 23.
Peterson pleaded no contest to misdemeanor reckless assault last Tuesday and was ordered to pay a $4,000 fine and perform 80 hours of community service. He originally faced felony charges of reckless or negligent injury to a child after being accused of hitting his 4-year-old son with a switch.
The NFL announced Thursday that it has informed Peterson his case will be reviewed for potential discipline under the personal conduct policy, and asked him to submit any relevant information. Peterson, who is on the Commissioner's Exempt list, must be reinstated before he is allowed to play again.
The NFLPA is expected to argue in its grievance that the NFL agreed to take Peterson off the list when his court case was resolved, pending discipline under the league's personal conduct policy.
The NFL released the following statement, acknowledging it had received the grievance:
"We have received the NFLPA’s grievance on behalf of Adrian Peterson. We have honored our commitment to Mr. Peterson and the NFLPA not to process or impose any discipline until the criminal charges pending in Texas were resolved. When Mr. Peterson decided not to contest criminal charges, we promptly advised both him and the NFLPA that we were prepared to consider what, if any, discipline should now be imposed under the Personal Conduct Policy. We asked Mr. Peterson and his representatives, including the NFLPA, for relevant information. We have not received any of the requested information, but remain prepared to schedule a hearing and make a determination as quickly as possible based on as much information as available."
On Sunday, CBS Sports' Jason La Canfora reported that there is no guarantee the Vikings will welcome Peterson back to the team if he is reinstated. La Canfora said Minnesota has "serious concerns" about the running back's physical and mental state and is sensitive to the backlash it will receive if Peterson returns.
NFL Network's Ian Rapoport reported the same day that Vikings executives are "divided" on whether they want Peterson to return if immediately reinstated.
On Tuesday, Ed Werder of ESPN reported that the case "could get ugly."
- Molly Geary