Manny Pacquiao -- Trading Shots With NBA Legends

Manny Pacquiao stepped out of the ring today and on to the blacktop ... where he took on TWO basketball legends at the same damn time.

TMZ has obtained a photo of Manny ballin' around with NBA gods Charles Barkley and Reggie Miller.

We're told the guys had been training all day long -- including a trail run in Griffith Park -- before they decided to hit a local court for a shootaround session.

Sources tell us cameras documented the entire thing for an upcoming special on TNT.