Lil B -- 'I'm Extremely Worried for James Harden'

James Harden may have just made things A LOT worse for himself ... because rapper Lil B is threatening to UP THE CURSE on the NBA star in the wake of a Harden smack talk session.

Lil B just appeared on "TMZ Hollywood Sports" and said Harden was straight up LYING when the NBA star told us he's never heard of Lil B and didn't steal his cooking dance.

So, what's gonna happen to Harden now? Watch the clip and find out ...

Check out "TMZ Hollywood Sports" weeknights on Reelz.