"Here you have a situation where the state party has sat back and done nothing and allowed this to happen," he told ABC Radio. "You're not going to get me defending it any shape or form."

Elected in 2016, Senator Hume is facing a potential preselection challenge from the party's federal vice-president Karina Okotel, a lawyer and a prominent campaigner against same-sex marriage last year, as well as Mormon doctor Ivan Stratov, both linked to hard-right factional powerbroker Marcus Bastiaan.

Senator Hume - who was speaking to branch members in Chisholm on Monday night as part of her efforts to retain her seat - would not comment on her preselection, but said of Ms Prentice: "It’s a tragedy to lose a meritorious woman."

One Victorian Liberal, speaking on condition of anonymity, said the Senate preselection process was democratic and likely to be messy, but Senator Hume was more likely to survive than not.

"I know she has irritated some people who supported her last time," the source said. “Jane was pitching herself as centrist or centre right. She has probably turned out to be more of a leftie Lib.”

Senator Hume is a target because of her support for same-sex marriage. James Paterson, also a Victorian senator, could be at risk but is considered more likely to survive.

Preselection threats have been rife in Victoria under state president Michael Kroger, including repeated attempts to unseat Financial Services Minister Kelly O'Dwyer - even while she was pregnant.

But on Monday a source close to the Kroger-Bastiaan camp played down the threat, praising Senator Hume’s work ethic and saying there was no appetite for major changes within the party.

"The aim is to win the election," they said - by winning seats, not in-fighting. The challenge to Mr Kroger at the recent state council meeting had been “change enough” in the past six months, the source said.

In NSW, Ms Sudmalis is reportedly facing a challenge from Grant Schultz, son of former Liberal MP Alby Schultz. Ms Sudmalis did not return calls on Monday.

Mr Turnbull, who advocated for Ms Prentice during the preselection but did not step in to save her, lamented her defeat but said it was "the consequence of having a grassroots political party".

Numerous Liberal frontbenchers, keen to spruik the party's gender credentials, pointed to the recent appointment of Amanda Stoker to the Senate to replace former attorney-general George Brandis.