Mac McClung is the back-to-back NBA Slam Dunk champion, but even he has his doubts about going at the King ... telling TMZ Sports he'd "probably" lose to LeBron James in a contest!!
The 25-year-old G League star wowed the crowd yet again during All-Star festivities this past weekend ... edging out Celtics star Jaylen Brown to take home the trophy in Indy.
We spoke with the high-flying athlete about what's next following his big victory ... and while he's planning to finish out this season strong before going back to the drawing board for new dunks, there's one thing you can probably take off his "To-Do" list -- a showdown with LeBron.