Federal Labor MP Mike Kelly has quit politics for health reasons, triggering a knife-edge by-election in his southern NSW seat.
The looming by-election in Eden-Monaro is expected to be a three-cornered contest with high-profile coalition members jostling for a crack at the marginal seat.
Bega mayor Kristy McBain is likely to run for Labor, while NSW Deputy Premier John Barilaro could run for the Nationals and is considered a strong chance to reclaim the seat for the coalition and give it a crucial buffer in the lower house.
But he could face a contest from within the coalition with NSW Transport Minister Andrew Constance and Senator Jim Molan touted as Liberal candidates.
Serious kidney issues and deteriorating osteoarthritis stemming from Mr Kelly's army service have hampered his ability to travel through his country seat of Eden-Monaro.
"I really do regret and it has broken my heart to do this. It's gut-wrenching," he told reporters in Canberra on Thursday.
Dr Kelly's renal system was damaged from severe dehydration during military tours in Somalia, East Timor, Bosnia and Iraq.
He apologised for distracting from the national crises of coronavirus and bushfire recovery, which is a major issue in his singed electorate.
"I certainly couldn't cope mentally with not being able to go full pace at this job," he said.
"My whole life of 36 years of public service has been body and soul into whatever I've done, and I'm sort of paying a bit of a heavy price for that at the moment."
The towering MP broke down as he thanked his family for their support.
Opposition leader Anthony Albanese and Prime Minister Scott Morrison have played down their parties' hopes of winning the seat.
Mr Albanese says the coalition are favourites because Labor mainly held the seat due to Dr Kelly's high personal standing in the seat, which he estimates is worth three to four per cent of the vote.
Mr Morrison points to history with the government last winning a by-election from the opposition in 1920.
Labor holds the seat with a margin of less than one per cent.
Mr Barilaro argues a three-cornered showdown isn't in the coalition's best interests.
The state Nationals leader has vowed not to run against Mr Constance as he weighs up the decision to run over the weekend.
"I can't rule it out, don't rule it in," he told Sky News.
Mr Barilaro's state electorate covers the Queanbeyan area, where the majority of the Eden-Monaro population lives.
"If I do this, I do this knowing I could be out of politics," he said.
Mr Constance on Thursday said he remained uncertain about whether he would try and make the switch to federal politics.
"For me, at the moment, give us a couple of days to think through it," he told reporters.
Eden-Monaro takes in the bushfire-hit town of Cobargo whose residents gave the prime minister an extremely hostile reception earlier this year.
Australian Associated Press