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Former UFC fighter Matthew Riddle -- who was fired for smoking weed last year -- is getting guidance on his new career path from a seasoned vet ... and we got the headlocked proof.

Riddle recently started training to become a pro wrestler at the Monster Factory in New Jersey ... where former WWE wrestler The Blue Meanie is keeping a close eye on his work.

Meanie tells us Riddle has been doing great in his first few days of training ... and Matthew is really enthusiastic about learning the craft.

We already came up with a nickname for him: The Riddler.