Khloe Kardashian has a brand new star athlete in her life ... Cleveland Cavaliers stud Tristan Thompson.

The two have been spending some serious quality time together recently ... and Thursday, they were spotted at a mansion in Beverly Hills ... flaunting their impressive physiques.

Unclear if they're friends ... or more ... but we did see them out at Bootsy Bellows nightclub together over the weekend ... and they left the club within minutes of each other.

One thing's clear ... they definitely look good together.