Liberal frontbencher Steven Marshall says he phoned former foreign minister Alexander Downer last night before announcing plans to stand for the South Australian Liberal leadership.
Isobel Redmond stepped down yesterday following months of speculation Mr Downer was interested in the leadership job.
Mr Marshall served as Ms Redmond's deputy since a leadership spill in October in which former leader Martin Hamilton-Smith was defeated by one vote.
Mr Marshall will remain acting leader until a ballot is held on Monday and confirmed his nomination in Port Pirie this morning where the party is holding a strategy meeting.
The first-term MP is understood to have cross-factional support and is expected to be elected unopposed.
He says he has spoken to colleagues and also sought an assurance from Mr Downer.
"He made it very clear that he's got no intentions to run for the Liberal party leadership whatsoever and he wished me well," he said.
"I wanted to find out from Mr Downer what his intentions were. He made them extremely clear."
Mr Marshall says he will not be running on a ticket on Monday and has not endorsed anyone for the deputy's position.
He says the party must be quick to put long-standing disunity behind it after the ballot.
"I haven't heard that anybody else will be running," he said.
"I've received a huge amount of support from my colleagues overnight."
Mr Marshall was elected to Parliament in 2010 but says he has the necessary experience to become Opposition Leader.
"I come to this job with a huge amount of experience in the commercial sector. I think that's a useful set of experiences to bring to the leadership role in the Liberal Party. We'll see what the party room decides on Monday."
Opposition frontbencher Rob Lucas says the speculation that undermined Ms Redmond must not continue after Monday's ballot.
"It is a clear message to a number of my friends and colleagues in the Federal Parliamentary Party, in the state organisation and elsewhere that it is the State Parliamentary Liberal Party that chooses its leader," he said.
"We cannot afford the view from those outside the State Parliamentary Liberal Party to continue after Monday morning."
Line of leaders
Ms Redmond told her colleagues yesterday of her decision to quit at the beginning of the two-day conference.
Opposition frontbencher Vickie Chapman will nominate for the position of deputy leader, while Mr Hamilton-Smith is also considering running for that post.
Mr Marshall's candidacy means a third of the Liberal Members of the House of Assembly have at one time nominated for the leadership.
The Liberals hold 18 of the 47 seats in Parliament.
Mr Hamilton-Smith became Opposition Leader in 2007 after successfully challenging Iain Evans for the position.
Ms Chapman challenged Mr Hamilton-Smith in July 2009 but lost that ballot, only for Mr Hamilton-Smith to step down less than a week later.
Ms Redmond defeated Ms Chapman in the subsequent spill.
Rob Lucas was also Opposition Leader from 1989 to 1993.
Political commentator Clem Macintyre says the Liberal Party needs to elect its next leader unopposed if it wants to heal its long-standing divisions.
"I think that would send a very positive signal to South Australian voters if whoever they unite around is elected unopposed," he said.
"The last leadership ballot in the Liberal Party was in October, Isobel Redmond won that by one vote and I think everybody at the time just shook their head and said that it was not really resolving the deep problems that they've had."