Vikings GM certain Peterson will regain his old form

From a pure football fan's perspective, one of the biggest disappointments of the 2011 season came in Week 15, when Vikings running back Adrian Peterson went down with a serious knee injury.

The official diagnosis was a torn ACL, and the four-time Pro Bowler had surgery in December to repair the ligament.

It's the type of injury most skill players in the NFL never make it all the way back from, but Vikings general manager Rick Spielman says Peterson will be the exception to the rule.

"He's not like most running backs that I've been around through my career," Spielman told ProFootballTalk.com on Thursday. "He is just a freak athletically and you can see that in his rehab and how quickly he's coming back from this ACL and I know he wants to go out there and prove to everybody he’s a better Adrian Peterson than he was before the injury."

Peterson signed a seven-year, $96 million contract last September, which means the Vikings could have a difficult decision on their hands if their star is slow to return to form. In 2013, Peterson's salary is set to jump from $8 million to $11.25 million.

That's superstar money for a player who now must prove he still warrants the designation.