'Sugar' Shane Mosley -- Something's Really Fishy About Don King's Paperwork (VIDEO)

It's the fight BEFORE the fight for 'Sugar' Shane Mosley -- his courtroom showdown with Don King -- and Mosley thinks King is trying to pull a fast one on the judge.

We got Mosley at LAX Wednesday night ... as he was jetting off to Miami, where he hopes to testify in federal court. As we've reported, King is suing to block Mosley from fighting Ricardo Mayorga. Don claims Mayorga's still under contract with him.

Shane tells TMZ Sports, "Don has some fraudulent stuff going on" -- and thinks the signatures on King's alleged contract with Mayorga don't match.

He also thinks there's a jurisdiction problem ... as in Don's not even in the right court!