Mr Constance withdrew from the contest after Mr Barilaro, his state colleague and NSW Nationals leader, described him as a "c**t" in a story in the Sydney News Corp press.

"Bugger this for a joke, why would I sit here for the next five weeks defending that kind of front page," Mr Constance said on Wednesday, explaining his sudden decision not to contest the byelection in the NSW coastal seat."

Mr Barilaro is reported to have used the profanity in a conversation with a party colleague last week when he and Mr Constance were both considering running.

"When I say politics is stuffed in this country and some of the people in it need to have a long hard look, I meant it - and we've now seen it in such as great way on the front page," Mr Constance said. "I mean stuff that. I mean seriously. I haven't signed up federally to be called that kind of smear."

Mr Constance said he had had a "gutful".

"If you get called that on the front page heading into a neck-and-neck byelection and that smear's there, how can you bring about the unity and clarity to be able to deliver that. I mean that type of white-anting doesn't just stop with that front page, it goes on and on so lets be realistic about it you can't sort of front up, hand on heart, say everything's ok. ... It's pretty poor, absolutely it's disappointing, it's humiliating."

Mr Constance said he had "cleared it up" in a conversation with Mr Barilaro and the pair remained mates but said he hadn't expected the attack.

He also apologised for the confusion over his sudden change of mind which left the Coalition's plans for the seat in turmoil.

On Friday, Mr Barilaro appeared to be the Coalition frontrunner, but Mr Barilaro changed his mind over the weekend - reportedly after internal party polling which suggested Mr Constance was the better candidate.

But in withdrawing from the contest, Mr Barilaro left destruction in his wake, first texting Nationals federal leader Michael McCormack telling him he was a failed leader - a text made public also through the conservative media - and then attacking Mr Constance with the profanity.

Mr Barilaro told Mr McCormack that his lack of public enthusiasm for his candidacy had gone a long way towards his decison.

"To feel threatened by me clearly shows you have failed your team and failed as a leader. You will never be acknowledged by me as our leader. You aren't. You never will be," his text message said.

Mr Constance was a high-profile local figure during the bushfire crisis on the NSW South Coast, when he was critical of Prime Minister Scott Morrison's response. His criticism of Mr Morrison would have complicated his candidacy, but his profile made him a strong candidate for the Liberals.

Liberal senator Jim Molan has also confirmed that he won't run for preselection for the lower house seat. The withdrawals leave truffle farmer Fiona Kotvojs as the only known candidate for Liberal preselection. Ms Kotvojs ran for the Liberals in the seat in 2019, and has confirmed her candidacy to The Canberra Times.

Mr Barilaro's spokeswoman said he would not revisit his decision, and it is unclear who will now put their hand up for Nationals preselection.

Veteran Labor campaigner Bruce Hawker said Mr Barilaro was "congenitally disloyal" and unlikely to be welcomed by Mr McCormack in federal parliament.

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"He's demonstrated that time and again, attacking other members of the government, always going off doing his own thing. There's a touch of the Barnaby Joyces about him," Mr Hawker said.

"I suspect there's been pressure not to have a three cornered contest and McCormack has been a happy participant in that and Barilaro's been strong armed," he said.

Mr Hawker predicted the byelection would go down to the wire, with Ms Kotjovs coming close to beating Labor's candidate Mike Kelly last time, and Labor running popular local mayor Kristy McBain this time.