Victorian Shooters, Fishers & Farmers MP Jeff Bourman has declared he will not back legislation allowing voluntary euthanasia.
His decision leaves supporters of the bill one vote short of the required numbers needed for it to pass, with Upper House Liberal president Bruce Atkinson the final undecided MP.
Parliament will debate the legislation today, although Mr Bourman said he would not speak on the bill.
"The construct of the bill doesn't provide me comfort," he told the ABC.
"This is life and death and I have enough concerns with the bill, not the principle, that I cannot support the bill."
As a former police officer, Mr Bourman said he also had problems with the non-reporting of an assisted death to the coroner in cases where the drug is administered by a doctor.
Mr Bourman said there had been immense pressure from both sides.
"I won't say it's been grubby, but it's been disappointing," he said.
The MP said it had been the toughest period of his professional life.
His party colleague, Daniel Young, also declared this morning he would not vote for the legislation.
There are 20 Yes votes in the 40-member Upper House so far, with 19 declaring they will vote No, although that includes Simon Ramsay who is seeking amendments which may change his vote.
