Adrian Peterson is back on the active roster, making him immediately available to play against the Indianapolis Colts on Sunday at U.S. Bank Stadium.

The Vikings announced Peterson's status upgrade Saturday. Defensive tackle Toby Johnson was waived to make room for Peterson.

The Vikings are battling for a playoff berth and have to beat the Colts to have a shot at the postseason.

Peterson would presumably improve those chances.

Peterson was aiming for a return Dec. 24 against the Green Bay Packers, but after three practices this week, he declared he was "ready to roll."

He needed full medical clearance after surgery in Sept. 22 to repair a torn meniscus in his right knee. The injury ordinarily requires a four-to-six month-recovery period. But as he did in 2012 when he tore his ACL, Peterson blew through the comeback schedule.

He plans to wear a knee brace. It isn't clear how much Peterson will play. In his absence, Matt Asiata and Jerick McKinnon have carried a league-worst run game that is averaging 3.0 yards a carry. The struggles have been especially evident near the goal line, where Peterson, even if not 100 percent, could make an immediate impact.

Peterson averaged just 1.6 yards per carry on 31 attempts before his injury. He returns to an offense that has changed a lot since he was injured in Week 2 against the Packers.

Pat Shurmur has replaced Norv Turner as offensive coordinator. The offense is feasting on short and quick passes to better protect Sam Bradford behind an injury-riddled offensive line that will feature it's seventh different starting lineup on Sunday.

The Vikings did take some deep shots in last week's win against the Jaguars, but overall, Peterson will need to be integrated into a new-look scheme that will require his patience.

"Obviously, it's a little bit different than the first couple weeks of the season," Bradford said this week. "But Adrian's a great player and I'm sure he'll be able to adjust. But also, probably just finding things that, obviously, he's comfortable with, runs that he likes that they've had success with in the past."

Peterson's very presence brings a big lift to a 7-6 team that still has a shot at the playoffs.

"The worst thing that could've happened was waiting a week and watching my team lose, which that's not what I expect," Peterson told Dash Radio on Friday.