Former party leader and deputy prime minister John Anderson said the political chaos sparked by the messy political divorce between the Nationals and Liberals meant neither party was able to do its job properly.
"The Nationals absolutely have to recognise the national imperatives here," Mr Anderson told AAP.
"This is not about individual manoeuvring or ploys to gain advantage.
"What we desperately need now is an effective opposition in the face of a government that is baking in long-term decline and is displaying a distinct lack of character."
Queensland Nationals MP Colin Boyce has declared he will move against David Littleproud when parliament returns next week, arguing the leader had twice "blown the coalition up" since the federal election in May and failed to provide stability.
"That is not a position I want to be in," he told ABC Radio on Thursday.
Mr Boyce admitted he had not begun canvassing colleagues for votes, insisting the spill motion was not designed to clear the way for another contender.
Senior Nationals members are confident Mr Littleproud will remain leader.
While Mr Anderson would not be drawn on the impending spill triggered by Mr Boyce, he urged the coalition to unify to restore the national interest and put the Australian people above politics.
"This is a serious, really serious situation for Australia. We are in serious decline as a nation and we've lost our direction," he said.
"A government won't perform without an effective opposition and an opposition that people actually believe can be taken seriously as an alternative government."
Influential senators Matt Canavan and Michael McCormack won't support the spill motion in the party room on Monday.
"The buck stops obviously with the leaders, so I hope David can keep everyone together," Senator Canavan told Sky News.
Ex-New England MP Tony Windsor, who was a member of the Nationals before he became an independent, said the party's turmoil had been driven less by policy disputes and more by a deeper struggle over relevance.
He said the party risked being "outnumbered in a few of the seats" if it broke away from the coalition.
Mr Windsor said the Nationals' infighting, alongside competition from One Nation and the Liberals, could open the door to a new wave of strong independent candidates in regional seats.
He singled out Darren Chester as the only figure he believed had the intellect and broad appeal to lead the Nationals effectively.
"He's got the brains to be a good leader and a common sense leader, but he's not part of that sort of radical Queensland," Mr Windsor said.
Mr Chester said he would not be throwing his hat into the ring
"The sooner the Liberals and the Nationals can resolve any internal leadership debates and set up a plan to transition back to a functioning coalition, the sooner we can hold this poor government to account," he said in a lengthy social media post.
The impending leadership spill is delaying Opposition Leader Sussan Ley's push for reunion talks with the Nationals.
Ms Ley wrote to her Liberal colleagues on Wednesday, saying she had asked to meet with Mr Littleproud and other senior party officials as a priority.
The opposition leader said it was in the national interest to maintain a strong and functioning relationship between the two parties, whether or not they were in a formal coalition.
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