Mr Pesutto is seeking to expel Ms Deeming from the parliamentary party after she spoke at British anti-trans activist Kellie-Jay Keen-Minshull's Let Women Speak event outside Victorian parliament on Saturday.
The rally was attended by members of the National Socialist Movement who repeatedly performed the Nazi salute and held signs calling transgender people offensive names, sparking violent clashes with hundreds of counter-protesters.
Mr Pesutto said Ms Deeming's expulsion was necessary because of her association with organisers with links to extremists, including neo-Nazis and white supremacists.
Ms Deeming suggested she wasn't aware of the links when the pair met on Sunday but Mr Pesutto finds that hard to believe.
"I don't think it's open to me to be satisfied that Moira didn't know about their history," he told reporters on Monday.
"It took us all of about 20 minutes or so after the rally on Saturday to investigate the histories of these people."
Mr Pesutto took umbrage with her decision to stay at the event when Nazi supporters showed up and celebrate afterwards with rally organisers, whom he said she led through the parliamentary precinct.
"I will never, ever accept any member of the parliamentary Liberal Party under my leadership ever associating with anybody who shares a platform with people who peddle hate, division and attack people for who they are," he said.
In a Facebook live video with organisers after the rally, Ms Deeming said other politicians were in the crowd.
"They didn't come up the front with me but they, to their credit, were there listening," she said.
Mr Pesutto said his advice was that no other Liberal MPs attended the rally but pledged to look into the matter.
Ms Deeming promoted the rally in parliament on March 8 but Mr Pesutto was adamant the Liberal leadership team was unaware of her participation and involvement until after Saturday's ugly scenes.
"I can't babysit every MP," he said.
The expulsion motion is expected to be put to a vote early next week and Mr Pesutto is confident it will pass, despite only narrowly winning a leadership ballot last year and reports of internal discontent.
The former teacher and City of Melton councillor will have an opportunity to plead her case to partyroom colleagues.
Ms Deeming was elected to the Victorian parliament last year as a member for Western Metropolitan, replacing veteran MP Bernie Finn after he was expelled over his controversial views on abortion.
Her position on transgender issues was openly canvassed before the election, with then opposition leader Matthew Guy describing her comments as "in the past".
She used her inaugural speech last month to call for an inquiry into transition practices and criticised measures to include trans women in female-only change rooms and sports.
At the time, Mr Pesutto said he didn't agree with the views but declined to reprimand her.
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