McCormack favourite for Nats leadership

Veterans Affairs Minister Michael McCormack is frontrunner to become the next deputy prime minister after confirming he will stand to replace Barnaby Joyce as Nationals leader.

The NSW MP will nominate for the leadership at Monday's party room meeting after Mr Joyce formally quits.

"I am a fighter and I have the drive to deliver," Mr McCormack said in a statement on Friday.

The Riverina MP, a minister since 2013, cited crossing the floor over water rights in his electorate and opposing a takeover of GrainCorp as examples of his leadership credentials.

Former infrastructure minister Darren Chester and Parkes MP David Coulton have publicly backed Mr McCormack.

"The new leader's going to need to heal some divisions which have developed," Mr Chester told Sky News on Friday.

"I think someone like Michael McCormack from Riverina can pull together the Queenslanders, the New South Welshmen, the Victorians and unite."

He has one confirmed challenger, fellow NSW MP David Gillespie.

Before Mr Joyce's announcement, Dr Gillespie said he was a safe pair of hands with ministerial experience and a record of delivering in his electorate.

The member for Lyne on the NSW mid-north coast was a gastroenterologist for 20 years before he entered parliament in 2013.

He was appointed assistant minister for rural health in 2016 then became assistant minister for health and is now assistant minister for children and families.

Mr McCormack was editor of the Daily Advertiser in Wagga Wagga during the 1990s and entered parliament in 2010.

Veteran Nationals senator John Williams said Mr McCormack would be a good fit and wished Dr Gillespie all the best.

"Michael's always been a good mate of mine. Works hard, well presented and does his job well, knows his job well," Senator Williams told Sky News.

"But there are probably several there that could do the same job."

Dr Gillespie faces a High Court challenge over an Australia Post outlet in a small suburban shopping complex he owns on the mid-north coast.

Although he has sold the post office since his election, the court could rule he is ineligible to sit in parliament if it finds he had an indirect financial interest in the commonwealth.

"If I thought I had a problem I wouldn't have stood for ministry and I wouldn't have continued standing," Dr Gillespie told reporters in his electorate on Friday.

Agriculture Minister David Littleproud is not expected to contest the leadership after being given a shock promotion to cabinet two months ago.

Mr Joyce has declined to publicly back any successor.