Cassie is ready to take the witness stand in Diddy‘s sex trafficking trial … and it sounds like it may be happening as soon as Tuesday … at least based on what her lawyer is telling us.

We got Cassie’s attorney Douglas Wigdor outside the federal courthouse where Diddy’s trial is going down and he told us she will be testifying “in very short order.”

Cassie’s name was brought up several times during opening arguments and the first day of witness testimony … including when prosecutors claimed Diddy made a male sex worker urinate in her mouth during a “freak off” she was forced to attend.

Cassie is pregnant and far along in her pregnancy, and her husband Alex Fine was in court Monday … and we asked Wigdor why Alex was there.

The first day of testimony featured a hotel security guard talking about the Cassie beating video and a male sex worker talking about the “freak offs” … but Cassie is the star witness and she’s expected to have the most important testimony.