Lil Wayne's Agency Sues NBA's Frank Mason, Gimme Back My Diamond Chai -

Lil Wayne wants his bling, bling back -- claiming NBA player Frank Mason ditched his Young Money sports agency ... and refuses to give back his YM chain.

Backstory ... Mason signed to Weezy's Young Money APAA Sports Group back in April 2017 ... right before the NBA Draft (he was selected in the 2nd round by the Sacramento Kings).

As part of the deal, YM says it advanced Mason $40,000, agreed to pay his pre-draft expenses (totaling $52k) and hooked him up with an $11,000 diamond Young Money chain. Pretty standard stuff.

The catch, YM says Mason's contract stated that if he ever left the agency, he had to repay the money and give back his jewelry.

Well, in April 2018 -- toward the end of Mason's rookie season -- Mason fired Young Money "at the urging of a former YM employee" but never gave back the stuff, according to a lawsuit obtained by TMZ Sports.

Now, Young Money is asking the judge to force Mason's hand -- demanding $92k in cash plus the chain PLUS damages.

FYI, Mason's NBA contract isn't super rich -- he only made $1.3 mil last season and will make similar money for the next 2 years.

What's interesting, Mason appeared on the "TMZ Sports" TV show right after he signed with Young Money and told the guys why he was pumped to be in business with Lil Wayne.

No word on what changed after the interview ...