Graham Chase Robinson claimed the Raging Bull star was verbally abusive and subjected her to unwanted physical contact and sexually-charged comments.

In response, his lawyer said the allegations were "beyond absurd".

The case comes weeks after De Niro sued Robinson, accusing her of misusing funds and bingeing on Netflix at work.

Her legal documents, which were published by US media on Thursday, said he "concocted false allegations" designed to prevent her from taking action and to destroy her career and reputation.

She started working as the star's executive assistant in 2008 and said he referred to her as his "assistant" despite two subsequent promotions.

'Abusive and intimidating'

He communicated with her in a "hostile, abusive and intimidating" way, she claims, including making "vulgar, inappropriate and gendered comments" towards her.

Her case said: "He would joke with Ms Robinson about his Viagra prescription. De Niro smirked to Ms Robinson about his young paramour, who was around Ms Robinson's age.

"De Niro directed Ms Robinson to imagine him on the toilet. He told Ms Robinson that doing manual labour would 'make a man out of you.' De Niro suggested that Ms Robinson could get pregnant using sperm from her (married) male co-worker."

He paid her less than a man, and asked her to do "stereotypically female" tasks like putting away his underwear, hanging up his clothes and vacuuming his apartment, she said.

The "gratuitous physical contact" involved him asking her to "scratch his back, button his shirts, fix his collars, tie his ties, and prod him awake when he was in bed", she said.

De Niro's lawyer told US media: "The allegations made by Graham Chase Robinson against Robert De Niro are beyond absurd."