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He's a legend in Minnesota ... and that's why Adrian Peterson was all about giving his former team a pump-up speech before the NFC Championship game!

The NFL superstar spoke with TMZ Sports ... telling us why he's truly excited and happy for Minnesota's success, despite the fact he now plays for the Arizona Cardinals.

And if the Vikings can ultimately win the Super Bowl, AP says he wouldn't turn down a ring from the team if they offered him one ... saying, "That would be awesome ... I did help build that stadium a little bit!"

There's more ... AP also updates us on his NFL future and how his body feels going into 2018.

Spoiler alert -- he ain't even close to hangin' it up!