Cassie's Lawyer Calls Diddy's Claim the Beating Tape Was Doctored BS

5:40 PM PT -- Diddy's legal team tells TMZ ... "Our written and oral communications with CNN’s counsel were clear - they destroyed the original video file they received from their source."

Cassie Ventura's lawyer is calling BS on Diddy's claim that the video of him beating her up in a hotel hallway is edited ... and, her attorney says he's sure the footage will be admitted into evidence.

Douglas Wigdor tells TMZ ... it's not surprising Diddy "would make a disingenuous argument to exclude the disturbing video from being shown to the jury in the upcoming trial."

Cassie's attorney adds ... "I am confident that the video fairly and accurately represents what happened, will be admitted into evidence" ... and Diddy "will be held accountable for his depravity."

TMZ broke the story ... Diddy's defense claims CNN destroyed the only known copy of the 2016 Cassie beating video and aired altered footage before destroying the original version.

Diddy's camp claims CNN purchased the video, uploaded it into a free editing software, altered the footage and then destroyed the original.

As for the alleged altering ... Diddy's defense claims CNN covered the time stamp, changed the video sequence and sped up the video to make it falsely appear like the actions in the video happened faster than in reality.

Diddy's team is filing legal docs to exclude the video from his upcoming trial, but Cassie's camp thinks his motion will be denied.