The Wagga Wagga-based MP and Veterans Affairs Minister is the the only declared candidate.
Lyne MP David Gillespie pulled out of the running on Sunday afternoon and another potential starter, Agriculture Minister David Littleproud, announced he would not contest the leadership just after 11pm on Sunday night.
The Nationals will hold an 8am meeting in the nation’s capital to deal with the issue.
The Assistant Minister for Children and Families was tipped as Mr McCormack’s key rival, however, Mr Gillespie publicly announced he would retract his nomination.
His announcement came hours after Deputy Nationals leader Bridget McKenzie raised the “traditional behaviour” on ABC-TV’s Insiders.
It leaves Mr McCormack as the only Nationals MP to publicly put their name forward for consideration.
Senator Williams backs McCormack
Mr McCormack, the Minister for Veterans Affairs, has been heavily tipped as the favourite to replace Mr Joyce since he announced he would step down on Friday.
One Nationals member who has gone public with his view on the leadership is Senator John Williams.
Asked by journalists whether Mr McCormack would make a good National Party leader, Senator Williams said: “I think he would”.
“There’s probably several others as well,” he said.
“Michael’s always been a good mate of mine, works hard, well presented, and does his job well, but there’s probably several who could do the same job.”
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Mr Joyce resigned on Friday, after almost three weeks of controversy which began with news that the Deputy Prime Minister was expecting a baby with a former staff member who had also been shuffled in and out of high-paying jobs in the offices of two of his colleagues.
CSU lecturer Dominic O’Sullivan said convention – but not the Constitution – dictated that the Deputy Prime Minister should come from the House of Representatives rather than the Senate.
Professor O’Sullivan said this was the reason Mr Joyce had given up his spot as a senator for Queensland and contested the seat of New England.
Former Nationals leader and Deputy Prime Minister Tim Fischer made headlines during his periods as Acting Prime Minister for "running the country from his farm at Boree Creek”.
Mr Fischer would not be drawn into debate but said he believed the party would rebuild after losing Mr Joyce as leader.
“There will be a renewal,” Mr Fischer said.