Bronwyn Bishop's decision to abandon Tony Abbott when his leadership hung by a thread is set to become a central issue of the Liberal preselection battle for her Sydney northern beaches seat of Mackellar.

Ms Bishop is facing an imminent challenge from hard-right forces loyal to Mr Abbott and still furious about the former Speaker's decision to vote for Malcolm Turnbull last September.

Fairfax Media understands Mr Abbott's campaign manager and president of the Warringah federal electorate conference, Walter Villatora, is poised to enter the race for Mackellar.

Mr Villatora, an activist for democratic reform inside the Liberal Party, who worked as an adviser to NSW Premier Mike Baird during the state Coalition's time in opposition, has told a number of senior Liberals that he will contest Mackellar. Nominations close Friday at 5pm.