A famous American magician has been forced to reveal a trick after a British participant claimed to have been injured during a performance in Las Vegas.

David Copperfield, the world's highest paid magician, is being sued by British tourist Gavin Cox who claims to have fell during a 2013 trick, leaving him with lasting brain and body injuries and more than $400,000 in medical expenses.

The 61-year-old magician claimed that disclosing performance secrets would financial damage him, but Judge Mark Denton ordered him to reveal the trick in order to explain how Mr Cox was injured.

Mr Copperfield's Lucky #13 trick, involves 13 members of the audience standing on stage before they disappear.

Stagehands with flashlights usher participants through dark curtains, down unfamiliar passageways, round corners, outdoors, indoors and through an MGM Grand resort kitchen in time to re-enter the back of the theatre for their "reappearance" during the show finale.

Mr Cox claims he fell in a construction zone while being led through the secret passageways.

Mr Copperfield's friend and executive producer, Chris Kenner, estimated the magician had performed the trick tens of thousands of times over 20 years but MGM Grand lawyer Jerry Popovich said it was no longer used to close the show.

Mr Copperfield said he safely walked through the same area Mr Cox allegedly fell as part of another illusion that did not involve audience participation and said he did not notice any "debris".

Las Vegas resort MGM Grand is also a defendant in the lawsuit, and claims its passageways were clear.

Mr Cox and his wife, Minh-Hahn Cox, are seeking unspecified damages in the negligence lawsuit.