Minnesota Vikings running back Adrian Peterson has been reinstated after a judge ruled in favour of the NFL Players Association against the NFL on his behalf.

US District Court Judge David Doty made his ruling after the union argued that NFL commissioner Roger Goodell acted outside of his authority last November by suspending the Vikings star.

Peterson was banned until April 15 for disciplining his four-year-old son last May, but the argument was that he should not be subject to the league's new personal conduct policy because it was not instituted until late August.

The 29-year-old would again be the league's highest-paid running back if he returned under his current contract, and he has gone on record as saying he doesn't believe he should take a pay cut.

Vikings coach Mike Zimmer and general manager Rick Spielman have both indicated that they would want Peterson to return to Minnesota.