Barnaby Joyce's claim to the leadership of the Nationals is gaining legitimacy after three former leaders of the party gave him their blessing.
Former deputy prime ministers Mark Vaile, John Anderson and Tim Fischer have all backed the Agriculture Minister's credentials to be Prime Minister Malcolm Turnbull's second-in-command, a position the Nationals leader fills under the Coalition agreement with the Liberals.
Warren Truss is tipped to step down from the position within weeks.
But Acting Opposition Leader Penny Wong has warned against elevating the "entertaining but erratic" Mr Joyce, saying he doesn't have the "sober and sensible" leadership style the country needs.
Mr Anderson, leader from 1999 to 2005 and Mr Joyce's campaign director when he switched from the Senate to the House of Representatives, said the member for New England has "got a lot to contribute".
"I know from personal experience that three years is a slightly limited apprenticeship but he's intelligent and he's determined," Mr Anderson told Fairfax Media.
"And his voice is going to be needed for rural and regional Australia in a city-centric cabinet."
Mr Fischer, who led the party from 1990 to 1999, said two factors were in Mr Joyce's favour.
"Firstly, if you have successfully won tough elections to both the Senate and the House of Representatives, that is excellent experience for being a good leader and has helped him be a good deputy leader," he said.
"Secondly, he won many points on the matter of Johnny Depp's dogs … that was the correct call."
In May, Mr Joyce sensationally threatened to destroy the Hollywood film star's two dogs, Pistol and Boo, after the pets entered Australia illegally.
Mr Anderson and Mr Fischer were unwilling to directly compare Mr Joyce with other rumoured contenders and emphasised the contest was a matter for the party room.
Mr Vaile said Mr Joyce was a conviction and retail politician who would bring a constructive economic perspective to the executive team.
"My view is that Barnaby's best attribute is that he wears his heart on his sleeve. There is never any ambiguity about what he thinks."
He noted there were rarely surprises in Nationals leadership contests, with the deputy leader usually inheriting the top job.
"There can be surprises in a leadership ballot and there are certainly others with the necessary skills but the advantage that Barnaby has is that he's been in cabinet for a number of years."
Mr Joyce told Fairfax Media on Thursday he was ready to lead the party when Mr Truss stepped down.
However, there is a defiant group inside the 21-member Nationals party room known as the Anyone but Barnaby faction. MPs Michael McCormack and Darren Chester have both been mentioned as alternative choices.
Senator Wong said Mr Joyce was unfit to hold Australia's highest office when Mr Turnbull was absent.
"Barnaby is pretty entertaining, but he is also erratic, and he simply doesn't have the sober and sensible approach to do public policy that the Australians expect from the holders of high office," she said.
Mr Anderson also backed calls for an additional Nationals cabinet position, saying the Coalition partnership needs "strengthening" and was over represented by "inner-city ministers".