Sydney newspaper the Daily Telegraph is appealing the decision in the high-profile defamation case brought against it by Oscar-winning actor Geoffrey Rush.

In April federal court justice Michael Wigney ordered News Corp to pay more than $850,000 – with the prospect of millions more – to Rush after finding the Daily Telegraph defamed the actor by alleging he “engaged in inappropriate behaviour” during a theatre production of King Lear.

In his judgment, Wigney said the reports in the Daily Telegraph were “in all the circumstances, a recklessly irresponsible piece of sensationalist journalism of the worst kind”.

He said the evidence given against Rush by his Lear co-star Eryn Jean Norvill was uncorroborated by fellow cast members and found she was “prone to exaggeration and embellishment”.

On Monday the Daily Telegraph reported the newspaper had filed an appeal, citing 16 grounds upon which it claims the trial was miscarried and that Wigney’s conduct of the case “gave rise to an apprehension of bias”.

According to the Daily Telegraph its appeal document says Wigney’s bias was on display in finding “that Ms Norvill was an unreliable witness prone to exaggeration and lacking in credibility”.

The judge’s assessment of Norvill’s character is one of 16 appeal grounds in support of the newspaper’s claim “that the conduct of the proceedings by the primary judge gave rise to an apprehension of bias”, the Daily Telegraph reports.

The Daily Telegraph front-page story, published under the headline “King Leer” in November 2017, reported the Sydney Theatre Company had received the anonymous complaint but provided no further details.

Follow-up articles were published the next day, which Wigney said “doubled down” on the story.

Rush sued the newspaper and journalist Jonathon Moran, claiming the articles conveyed the imputation that he was a “pervert”, a “sexual predator” and “committed sexual assault”.