Following Friday's failed vote for Mrs Deeming to rejoin his team, the Victorian opposition leader announced a "definite absolute majority" of party MPs wanted her readmitted and called a second special meeting for January 15.
However, senior Liberal MPs Sam Groth, Richard Riordan, James Newbury, Brad Battin and Bridget Vallence have since signed a petition for the meeting to be held on Friday.
Four are members of Mr Pesutto's shadow cabinet.
Mr Groth quit his shadow cabinet post following Mr Pesutto's refusal to stand down after the Federal Court ruled he defamed Mrs Deeming and ordered him to pay $315,632 in damages plus costs.
A Pesutto ally, speaking to AAP on condition of anonymity, expects a leadership challenge to occur during the meeting or before the end of 2024.
"We'll see a new leader - I have no doubt about that," the Liberal MP said.
Mr Battin, a former police officer who unsuccessfully ran against then-incumbent opposition leader Michael O'Brien in 2021, has been touted as the frontrunner to replace Mr Pesutto.
On Friday, Liberal MPs were split 14-14 on whether to welcome Mrs Deeming back into the parliamentary party after she was expelled over a controversial rally she attended in March 2023 that was gatecrashed by neo-Nazis.
John Pesutto said he would move to readmit Mrs Deeming during a special meeting in mid-January. (Con Chronis/AAP PHOTOS)
A day after saying the party was "moving on", Mr Pesutto said he would move to readmit Mrs Deeming.
"There is now a definite absolute majority of my colleagues who want this issue resolved with her readmission so that we can collectively put this behind us and concentrate on the Prahran and Werribee by-elections and holding the Allan Labor Government to account," he said on Sunday.
"I again apologise to Mrs Deeming as we all work together to ensure the Liberal Party succeeds in winning government in November 2026."
It marked an about-face from Saturday, when Mr Pesutto denied his colleagues had given him an ultimatum to resign and said the matter was "resolved".
Mr Pesutto used his casting vote to break the 14-14 tie, although he argued it was technically not required because the motion required more than half of the party's 30 members to pass.
Mrs Deeming, who remains a Liberal party member but sits as an independent MP in the state's upper house, used an interview on Saturday to call for the leader's head.
"To treat me as some vengeful witch that needs to be burned at the stake is just incredibly offensive," she told Seven News.
Former Liberal prime minister Tony Abbott labelled Friday's vote a "shameful decision". (Mick Tsikas/AAP PHOTOS)
Former prime minister Tony Abbott earlier attacked the Victorian Liberals who voted against her readmission on Friday.
"How can someone elected as a Liberal be expelled on the basis of a lie and not be readmitted once the truth is there for all to see?" the former Liberal prime minister posted on X.
"Especially right before Christmas, the season of goodwill, this is a truly contemptible failure to act with honour and decency."
The internal upheaval stems from Mr Pesutto being found to have made defamatory comments implying Mrs Deeming was associated with Nazis following the Melbourne rally.
She was initially handed a nine-month suspension before being booted from the parliamentary party after threatening to sue Mr Pesutto.
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