Top NBA Rookies -- Mayweather Gave Us The Cold Shoulder ... In Cryo-Training

What do you do in Vegas when you have a couple million dollars but you're too young to get into any casinos?

If you're NBA rookies Karl-Anthony Towns and D'Angelo Russell you spend your days doing some seriously frosty training cues from the sports king of Vegas ... Floyd Mayweather.

Towns and Russell -- the top picks in this year's draft -- took a break from the NBA summer league recently and visited Floyd at his TMT gym to grab some pointers on being a superstar pro athlete.

Mayweather did more than just talk to the pair of pups ... he brought them to SubZero Recovery -- the state of the art cryo-lab he uses to bounce back during training ... and actually put the guys in the freezer.

The Cryo sessions last 90 seconds to 3 minutes ... and according to the guys at SZR, it helps to enrich blood, expel toxins and other cool stuff that helps to heal the body.

Welcome to the big leagues boys.