Metta World Peace: I'm Joining BIG3 League!!

Metta World Peace just casually dropped some BIG basketball news ... telling TMZ Sports he's gonna suit up for Ice Cube's 3-on-3 league next season!!

Metta -- who's already part of Master P's Global Mixed Gender League -- says he's gonna play for BOTH organizations ... on top of being a player developmental coach for the Lakers' G-League affiliate.

It's awesome news for BIG3 fans ... as the rest of next season's new players have yet to be revealed.