'Baby Joe' Castaneda Signs Celebrity Boxing Contract to Fight Adrian Peterson

Round II between Adrian Peterson and his poker rival looks like it will, in fact, go down inside a ring ... as TMZ Sports has learned the NFL legend's adversary has signed a contract with Celebrity Boxing.

The promotion's founder, Damon Feldman, tells us ... Joe "Baby Joe" Castaneda agreed to a scrap with Peterson this week -- and formally put pen to a pact on Tuesday.

Peterson's yet to ink his deal ... but Feldman tells us he's expecting that to happen soon.

It, of course, will be a rematch from May 27 -- when the guys duked it out at a social club in Houston, Texas over a hand of cards.

Castaneda told us Peterson had been trash-talking one of his friends while sitting at the felt ... and when he called for the ex-Vikings running back to stop, "that's when the melee kind of broke out."

Both guys were injured in the dispute, but they've each admitted they have no lingering bad blood toward one another -- which ultimately seems to have paved the way for their upcoming bout in between the ropes.

No fight night date has been set just yet ... but Castaneda said in a statement to us on Tuesday, "Time to get in shape and sharpening up these hands to put on a show!!!"