Tony Abbott not endorsing Bronwyn Bishop in preselection battle

Former prime minister Tony Abbott has confirmed he won't be endorsing his beleaguered ex-colleague Bronwyn Bishop for pre-selection in the Sydney seat of Mackellar.

Mr Abbott has said he will instead back close friend and business consultant Walter Villatora, who will be contesting for Ms Bishop's electorate at this Saturday's pre-selection.

"I'm not going to make any adverse comments on my colleague, my colleague of very long standing," Mr Abbott told the ABC's 7.30 on Thursday.

"Obviously I do know some of the candidates in the Mackellar pre-selection," he said.

"One I've worked with very, very closely and I respect very much, and that's why I've given him a reference.

"But in the end it's up to the pre-selectors of Mackellar to make what they think is the best choice."

Mr Abbott and Ms Bishop fell out last year after she resigned as Speaker amid a high-profile expenses scandal over her use of a $5000 chartered helicopter flight to attend a party fundraiser.

Ms Bishop later voted for Prime Minister Malcolm Turnbull during the leadership coup last September.

Other contenders for the northern Sydney seat include veteran Liberal Party member Jason Falinski.

Ms Bishop has reportedly faced pressure from party members within the seat and at the top of the party to retire.