A US judge says Elon Musk must face a defamation lawsuit by a British diver who said he was falsely branded a pedophile and child rapist by the chief executive of electric car company Tesla Inc.

US District Judge Stephen Wilson in Los Angeles said a reasonable jury could conclude that Mr Musk’s comments were more than merely opinions, and scheduled a trial for October 22.

The judge had on April 26 denied Mr Musk’s bid to dismiss the lawsuit brought by diver Vernon Unsworth, without explaining his reasoning.

Mr Musk’s lawyers did not immediately respond on Friday local time to requests for comment.

Mr Unsworth, who said in his lawsuit he shared a house in the Thailand countryside with a 40-year-old woman who owned a nail salon, was part of a team that helped rescue 12 boys and their soccer coach from a Thailand cave on July 10 last year.

He said he became a target for Mr Musk after saying on CNN that a mini-submarine offered for the rescue by Musk from his company SpaceX, where he is also chief executive, was a “PR stunt” and that Mr Musk could “stick his submarine where it hurts”.

Mr Musk later called Mr Unsworth “pedo guy” on Twitter, a comment for which he apologised.

He also urged a BuzzFeed News reporter by email to investigate Mr Unsworth and “stop defending child rapists.”

Mr Unsworth has denied those allegations.

In seeking a dismissal, Mr Musk’s lawyers said such comments were “imaginative” or “over-the-top” insults that constituted protected opinion under the US First Amendment.

But the judge said Mr Musk was not communicating in “heated and volatile” settings that might explain any excesses.

Mr 
Unsworth is seeking at least $US75,000 ($107,100) in compensatory damages plus punitive damages in his September 2018 lawsuit.

-AAP