The political future of Deputy Prime Minister Michael McCormack hangs in the balance amid an insurgent push to reinstate Barnaby Joyce into the Nationals leadership.

Key points: Matt Canavan quits the frontbench to back Barnaby Joyce's bid to return to the party leadership

Matt Canavan quits the frontbench to back Barnaby Joyce's bid to return to the party leadership Mr Joyce has confirmed he would challenge incumbent Michael McCormack on Tuesday

Mr Joyce has confirmed he would challenge incumbent Michael McCormack on Tuesday The party meeting was originally planned to replace outgoing deputy Bridget McKenzie

Cabinet Minister Matt Canavan late on Monday called Nationals leader Mr McCormack to offer his resignation from the frontbench to back Mr Joyce's push.

In a late twist, Senator Canavan said he had also referred himself to the Prime Minister over a possible conflict of interest having failed to disclose a membership.

Mr Joyce had earlier in the day said he would challenge for the leadership if the top job was spilled.

Queensland backbencher Llew O'Brien has said he would call for a spill of the leadership in Tuesday's partyroom meeting, which was originally planned to replace Bridget McKenzie following her resignation from the frontbench.

Senator Canavan said he wanted Mr Joyce to return to the leadership to give the Nationals a more forceful voice in Government.

"We are here to defend regional Australia … our constituents are under constant attack. We need a bulldog, we need a fighter to fight back against those who want to take away people's coal jobs, who want to shut down cane farms," Senator Canavan said.

"I do think a change in direction here will allow us to do that better.

"He is an effective fighter and that's why I'm backing him."

Matt Canavan announces offered his resignation pending the outcome of a leadership ballot. ( ABC News: Ian Cutmore )

While Senator Canavan has offered his resignation, it is yet to be accepted. It remains unclear if he will offer to resign to the Prime Minister.

He later said in a statement that his offer was "pending a ballot" for leader.

When asked if he would seek to stay on the frontbench if Mr McCormack wins, Senator Canavan refused to answer what he called a "hypothetical".

For the spill to be successful, it will need someone to move it and be seconded.

If that happens, there needs to be a simple majority of the 21-member partyroom for the leadership to be vacated.

The whip would then call for nominations and the party would vote on its leader.

Canavan failed to disclose membership

In announcing his support for Mr Joyce, Senator Canavan also said he had failed to disclose a membership that had come to his attention in the last week.

"I recalled that I had signed up as a regional supporter for the North Queensland Cowboys a number of years ago. I have not declared that interest," he said.

"In November last year, the Northern Australia Infrastructure Facility announced a loan, an investment, to the North Queensland football Club.

"I don't have any control, influence over the football club itself, but at the same time it is an interest I should have declared and I have not.

"I've taken the first opportunity to disclose it here and I will do the same in the Senate. I have sought advice from the Prime Minister office about it. I don't believe there is a breach of ministerial standards."

Bridget McKenzie said she expected a "Melbourne Cup field" of candidates seeking to replace her. ( ABC News: Sean Davey )

Senator McKenzie ultimately lost her job for failing to disclose membership to a club she awarded a sports grant to.

Sources have told the ABC the difference between the two cases is that Senator Canavan only had the power to veto funding, rather than allocate grants.