Adrian Peterson's Opponent Training On Video For Celeb Boxing Match

Joe Castaneda has already put hands on Adrian Peterson, but "Baby Joe" isn't taking the NFL legend lightly ahead of their Celebrity Boxing match ... he's started working out with a trainer, and TMZ Sports has the video!

We're told Castaneda -- a professional poker player by trade -- hired combat sports coach Teddy Concepcion at the Oasis gym in Las Vegas ... and Joe is already on the ground, going through a bunch of different drills, including hitting mitts.

It should come as no surprise that he's taking the fight seriously. Earlier this month, Castaneda told us this was the plan, saying he wanted to sharpen "up these hands to put on a show!"

He added ... "Baby Joe is here for all the smoke!!!"

As we previously reported, both Castaneda and 40-year-old Peterson, a future first-ballot Hall of Famer, have signed with Celeb Boxing.

The promotion's founder, Damon Feldman, is currently working behind the scenes to build out the event -- including finding a venue and broadcast/streaming partners.

Of course, when AP and JC step into the squared circle, it'll be a rematch.

The men first scrapped at a poker spot in Houston in May after a disagreement at the table ... and we obtained the shocking video.

Despite Adrian being an otherworldly athlete, both guys got some licks on the other ... in what was a relatively evenly matched brawl.

As for Peterson, it's unclear if he has started training ... though Adrian has some boxing experience after fighting Le'Veon Bell in a 2022 exhibition.