The club is Playhouse in Hollywood -- and sources tell TMZ, bouncers sent Drake on his way Wednesday night because CB was already partying at a table inside ... and they wanted to avoid any possible brawl scenarios.
According to sources, Brown was inside the club celebrating an anniversary party for some clothing brand called Popular Demand.
The bouncers were aware Chris was inside when Drake showed up around midnight ... and they knew Rihanna would be joining him later on ... so they asked Drake to party somewhere else that night.
The promoters -- and the nightclub -- obviously wanted to avoid what happened at W.i.P. nightclub last summer ... when Chris and Drake's entourage nearly destroyed the place with flying bottles.
We're told Drake handled the rejection like a gentleman and left without incident.