Chris Brown: Threatening, 'High on Drugs' ... Claims Ex-Tour Mgr.

Chris Brown allegedly cornered a female tour manager and went on a threatening, drug-fueled tirade so intense, she jumped off the tour bus and quit on the spot.

Sources connected to Chris' tour tell us the incident went down May 23 during Chris' European tour. Nancy Ghosh -- who's worked with the likes of J Lo, Kanye West and Justin Bieber -- claims Brown cursed her out in a dispute over her employment terms.

The day after the incident she fired off an email to Brown's team ... in which she explained she felt unsafe because Chris has been "irrational and high on drugs." Ghosh also claimed Brown referenced "what he did to Mike G" ... and threatened to do the same to her. TMZ broke the story ... Chris' ex-manager, Mike G, sued him for an alleged beatdown.

Ghosh said she refused to stay on the bus after the argument out of fear for her safety.

We're told a production manager on the tour also complained, through his lawyer ... claiming Brown has been verbally abusive and threatening.

We've reached out to Chris' camp ... so far no word back.