Matt Barnes Dishes on Business Meeting with Joe Montana

Matt Barnes' next move towards becoming a billionaire?? Settin' up business meetings with Hall of Famer Joe Montana!!

TMZ Sports spoke with the retired NBA star -- who recently told us he has a plan to join the 3 comma club by age 50 -- and he reveals how the 49ers legend might have a role in reaching that goal.

Barnes met with Montana at his investment firm earlier this week to discuss future collaborations ... and it must've gone well, 'cause he says they plan to meet again soon.