What happens in Vegas doesn't happen at Houston Rockets camp ... and that may be why James Harden has yet to join his team.
The NBA superstar has been partying it up in recent days -- from ragers with rapper Lil Baby on Thursday to reportedly hitting up Drai's nightclub in Sin City on Sunday night.
It sounds like a hell of a time, except the Rockets expected Harden to show up for an individual workout on Sunday ... but later told staffers he would arrive to camp "soon."
Of course, players are required to quarantine in their home markets before joining the team .