Cassie Sports Big Baby Bump as Diddy Trial Testimony Looms in New York

Cassie is set to testify against Diddy in his federal trial ... and, it better be sooner rather than later -- 'cause it looks like she may need to rest, recuperate and get ready for baby number 3 soon!

Photogs snapped Cassie out in New York City Wednesday ... standing on a stoop in a gray sweater that just barely covers her massive baby bump.

It's hard to tell exactly how far along the singer-songwriter is here, though she did announce she's with child back in February ... but, it's clear she's deep in pregnancy mode now -- and, she'll be waddling up to the witness stand soon to testify.

As you know ... Cassie is one of four alleged victims set to testify against Diddy -- and, she's the only one who will not be using a pseudonym or otherwise remaining anonymous during proceedings.

Cassie's a star witness for the prosecution ... 'cause she dated Diddy for more than a decade -- and, her civil lawsuit and cooperation with the federal government against Diddy seem to have contributed to his eventual arrest.

Jury selection in Diddy's trial kicked off earlier this week ... and, there are now 45 prospective jurors in the jury pool.

Court isn't in session today ... but, they're back tomorrow -- and, they plan on whittling down the pool from 45 to 12 jurors and six alternates.