An up-and-coming actor is set to testify in her defamation battle against Hollywood star Rebel Wilson over social media posts she claims painted her as a liar.

Charlotte MacInnes is suing the Pitch Perfect actor over social media posts claiming MacInnes had complained about feeling uncomfortable after bathing with the film's co-producer Amanda Ghost.

MacInnes alleges the posts - which could be seen by Wilson's 11 million followers for 24 hours - suggested she had withdrawn the alleged complaint in exchange for plum acting and music opportunities.

She denies making the complaint to the Bridesmaids actor and says her reputation has been seriously damaged before she could enjoy the benefits of starring in her first feature film.

The 26-year-old is expected to testify in the Federal Court in Sydney on Wednesday afternoon.

MacInnes stars in Wilson's film The Deb, a musical comedy set in rural NSW.

She was hailed by The Deb's co-writer Hannah Reilly as a talented, enthusiastic, and bubbly actor who has been irrevocably "hardened" by the social media posts.

In an affidavit tendered to the Federal Court, Ms Reilly wrote that MacInnes confided the posts had taken away some of her innocence and trust in the world.

The young actor said she was experiencing vivid nightmares, panic attacks, and stopped eating for days at a time.

"She has expressed to me that it has been an all-consuming nightmarish force in her life," Ms Reilly wrote.

She felt MacInnes had needed to become more armoured as a result of Wilson's social media posts, which she reported left her with a constant sense of vigilance and anxiety.

Prior to September 2024, the young actor had a reputation as a "bright star in the making", Ms Reilly wrote in her sworn statement.

She thought Wilson's subsequent social media posts suggested MacInnes was a liar who traded sexual favours to secure a role and a record deal.

Wilson maintains the young actor made the complaint before retracting it in order to ensure her future as a performer by appeasing Ms Ghost.

But MacInnes's friend and fellow actor Katelin Koprivec slammed the claim as "untrue" in her own affidavit tendered to the court.

"I knew how hard Charlotte had had to work to get the role, auditioning multiple times and proving herself to (a) panel of creatives," she wrote.

MacInnes felt Wilson was "bullying her in subtle ways" on the set of The Deb after the incident with Ms Ghost in September 2023, Koprivec said in her statement.

MacInnes had been devastated by the subsequent social media posts, her friend wrote.

MacInnes claims her professional reputation has been ruined by suggestions she is untrustworthy and prioritised her own career over those of the 300 cast and crew who worked on The Deb.

But Wilson's barrister Dauid Sibtain SC said in his opening statement MacInnes hadn't suffered any harm to her career at all since the social media posts.

The Deb was released in Australia earlier in April after legal issues prevented its widespread release following its 2024 film festival premiere.