The former political staffer was due to learn on Thursday whether his defamation case over reports of his alleged rape of Brittany Higgins had succeeded.
But, with his draft judgment printed and ready to be read out, Justice Michael Lee on Tuesday agreed fresh evidence concerning leaked text messages should be admitted.
"This is clearly fresh evidence," he said in the Federal Court on Tuesday evening.
A further hearing will be heard on Thursday, with judgment delayed at least a week.
Ten said the potentially case-changing evidence came from a television producer who had worked to secure an exclusive interview with Lehrmann for network rival Seven.
It included an allegation that Lehrmann, 28, provided the producer more than 2300 pages of "deeply personal exchanges" between Higgins and her former boyfriend, in breach of the longstanding rule in legal practice known as the Harman undertaking.
Lehrmann received the material, going back years, while defending himself in a criminal trial.
Lawyer Steven Whybrow and former Liberal staffer Bruce Lehmann arriving at the Federal Court of Australia in Sydney on 22 December, 2023. Source: AAP / Mick Tsikas
Ten's barrister Matthew Collins accused Lehrmann of giving his barristers instructions "that must have been wrong".
His barristers had previously told Ten and the court the undertaking concerning Higgins' messages had not been breached.
"This is not a trivial matter," Collins said.
"If the (producer) evidence is accepted, our submission will be it's a very serious matter."
Lehrmann, a former political staffer, is suing Ten and journalist Lisa Wilkinson over a February 2021 report on The Project where Higgins was interviewed about her alleged raped in a Parliament House office in March 2019.
He is seeking extensive damages, saying those reports have destroyed his reputation.
Lehrmann denies raping Higgins.
His barrister on Tuesday urged Justice Lee to dismiss the last-minute application, saying both his client and Higgins had told many lies on oath.
"It's really lipstick on a pig," barrister Matthew Richardson said.
"This stuff is trivial, it's just not relevant and to give leave to reopen on that sort of material would be inappropriate."
