Cassie Rushes to Court Over Ex-Male Escort's 'Threats' on Social Media

Cassie says she's being harassed and threatened by an ex-male escort who used to be hired for her freak-offs with Diddy ... and now she wants a judge to step in and help her ... TMZ has learned.

Cassie's lawyers fired off a letter Thursday to the judge handling a lawsuit Clayton Howard filed against her ... and in the note, obtained by TMZ, Cassie says Clayton posted a video on social media last week where he allegedly made threats against her ... including, "Bitch, I'm going to burn you out with fire."

Clayton allegedly added ... "You want to play stupid games, you can win stupid prizes." Cassie's lawyers insist the comments constitute true threats of violence.

In his lawsuit, Clayton claims he suffered injuries from the sex parties with Diddy and Cassie. Remember, he was one of the former male escorts who testified about freak offs during Diddy's criminal trial.

Cassie's legal team also claims Clayton went on social media and called Cassie a "whore" ... which they say is victim-blaming language.

The singer's attorneys claim Clayton is carrying out a public campaign to harass and intimidate her.

Cassie, who is now living abroad, is asking the court to set a hearing where she'll argue for an order prohibiting Clayton from trashing her.