The Los Angeles County Sheriff's Department said in a statement that the alleged incident involved an adult male.

The department said it began investigating the matter on December 11 and presented its results to the district attorney last week, five months after Spacey was fired from Netflix political drama "House of Cards" over sexual misconduct accusations.

A spokeswoman for the actor, Laura Johnson, declined to comment.

The nature and origin of the sexual assault accusation was not disclosed. It was unclear if California's statute of limitations on prosecuting criminal sexual assault, which is normally 10 years, would apply.

More than 30 men have said they were victims of unwanted sexual advances by Spacey, one of the most prominent Hollywood figures to be publicly accused of sexual misconduct since accusations against movie producer Harvey Weinstein sparked the #MeToo movement on social media.

Spacey, 58, became embroiled in controversy last year when actor Anthony Rapp accused him of trying to seduce him in 1986 when Rapp was 14.

Spacey later apologised for any inappropriate conduct while denying any specific memory of the behaviour in question.

The "American Beauty" actor also came under fire for using the occasion to acknowledge for the first time that he was gay, a statement gay advocates criticised as conflating issues of sexual wrongdoing with sexual orientation.

The fallout resulted in Spacey being dropped from the sixth and final season of the Netflix series "House of Cards," and erased from the 2017 movie "All the Money in the World." Christopher Plummer was brought in take over his role and reshoot all of Spacey's scenes.

London's Old Vic theatre, where Spacey served as artistic director for 12 years, said last year that it received 20 accusations of inappropriate conduct by Spacey between 1995 and 2013.

Australian Associated Press