Tito Ortiz says he's been contacted by someone connected to Mike Tyson to set up a fight ... and tells TMZ Sports straight-up, "I'm in!"
The 45-year-old UFC Hall of Famer says he got the call recently after watching some of the new Tyson training videos and believes a tilt with Iron Mike could be "the opportunity of my life."
Ortiz -- an MMA legend -- says he doesn't know if Mike is interested in boxing or a mixed martial arts fight ... but he's down either way.
Tito says he's been boxing for 20 years as part of his MMA training and thinks at this point in their lives, he's better in the ring than Mike who hasn't been in a pro fight since a 2005 loss to Kevin McBride.