Former speaker Bronwyn Bishop's preselection chances have been dealt a blow, with both Tony Abbott and New South Wales Premier Mike Baird writing references in support of a party official expected to run against her.

Walter Villatora is a former campaign director for Mr Baird and president of the Warringah federal conference, in Mr Abbott's seat.

He is expected to join a strong field to nominate for Liberal preselection in Mrs Bishop's Sydney seat of MacKellar, with nominations to close at 5:00pm this Friday.

Former prime minister Mr Abbott stood by Mrs Bishop during the "choppergate" scandal, enduring weeks of political damage, before she was finally forced to resign as speaker.

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Mrs Bishop then switched her support to Malcolm Turnbull, when he challenged Mr Abbott to become prime minister.

A spokesman for Mr Abbott confirmed he had written a reference for Mr Villatora "in the last week or so", but added it was "a general reference".

"How Walter uses it is up to him," the spokesman said.

Former premier weighs in on battle for Robb's seat

Meanwhile, former Victorian Liberal premier Jeff Kennett has backed the daughter of former foreign minister Alexander Downer in the Melbourne seat being vacated by retiring Trade Minister Andrew Robb.

Georgina Downer, a former lawyer and diplomat, is expected to nominate for the safe Melbourne seat of Goldstein.

Her father and grandfather were federal ministers and her great-grandfather was premier of South Australia.

Mr Kennett said he had come to know Ms Downer as a fellow board member, and his support was not due to the Downer dynasty.

"It's got nothing to do with that whatsoever," Mr Kennett told AM.

"She's very focused, she's very well educated, I think she would be a valuable addition to our parliamentary ranks."

The former Liberal leader also criticised the outgoing Human Rights Commissioner Tim Wilson, who did a round of media interviews yesterday, confirming his plan to resign at the end of the week to nominate for preselection in Goldstein.

Party rules do not allow candidates to promote themselves publicly.

Mr Wilson was careful to focus on the job he was leaving, although he did speak about why he wanted to enter Parliament.

He also spoke about his view that the Parliament, rather than a plebiscite, should decide on same-sex marriage — contrary to the Government's position.

Mr Kennett accused him of "playing on a technicality" for taking the opportunity to do interviews, before he rejoins the Liberal Party and lodges his nomination.

"I think that is probably unfair to the others and not in the spirit of the rules that govern the way members operate," Mr Kennett said.

Mr Wilson is considered by some party insiders as the leader in the preselection race.