The manager of the nightclub where Ruby Rose says she was allegedly sexually assaulted by Katy Perry more than 15 years ago is weighing in on the claim.

A former manager of the since-closed Spice Market nightclub in Melbourne, Australia told the Herald Sun that he never saw the alleged incident ... but confirmed Ruby and Katy were at the establishment that night and both "had way too much to drink."

As we reported ... Ruby posted a series of messages Sunday on Threads, claiming Katy had "rubbed her disgusting vagina on my face" while they were at a nightclub in Australia. Ruby, who is 40, said she was in her early 20s at the time and vomited during the alleged sexual assault.

Katy immediately hit back, telling TMZ through her rep ... "The allegations being circulated on social media by Ruby Rose about Katy Perry are not only categorically false, they are dangerous, reckless lies."

Again, the manager said he did NOT witness the alleged incident happen and knows nothing of anyone vomiting that night, but said Katy and Ruby left on good terms despite being heavily intoxicated.

According to Katy's rep, "Ms. Rose has a well-documented history of making serious public allegations on social media against various individuals, claims that have repeatedly been denied by those named."