Axl Rose is denying a claim of sexual assault that a woman just levied against him in court -- saying it's complete fiction ... and he's never heard a peep about the incident until now.

The rocker's attorney, Alan Gutman of Gutman Law, tells TMZ ... "Simply put, this incident never happened. Notably, these fictional claims were filed the day before the New York State filing deadline expires."

Gutman continues ... "Though he doesn’t deny the possibility of a fan photo taken in passing, Mr. Rose has no recollection of ever meeting or speaking to the Plaintiff, and has never heard about these again fictional allegations prior to today."

Finally, he finishes with this ... "Mr. Rose is confident this case will be resolved in his favor."

In other words, Axl's writing off Sheila Kennedy's allegations as totally made up -- and more importantly, he's suggesting this is only being filed right now to be able to capitalize on a key window regarding the statute of limitations pertaining to alleged sex abuse victims in NY.

TMZ broke the story ... Kennedy detailed an alleged incident she claims went down in 1989, when she says she was partying with Axl ... which she claims turned violent when AR allegedly tied her up and sexually penetrated her anally without her consent.