Phoebe Roberts, who was a body double on the set of Schreiber and Toni Collette's latest movie Mental, was believed to have spent a night with the star at his rented apartment after they were reportedly seen leaving a wrap party together last month.
Roberts told the Herald Sun: "I did not and am not having a sexual relationship with Liev Schreiber.
"We have a professional relationship. We worked together on a film and nothing inappropriate occurred between us."
Schreiber's spokesperson described the claims as "complete fabrication" earlier this week and confirmed that his solicitor is considering legal action.
Watts and Schreiber have been together since 2005 and have 4-year-old Sasha and 2-year-old Samuel together.
The Dirty, the website that first made the allegations, had quoted two Australian sources as saying that the rumours are "100%" true.
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