Anthony Albanese could soon be elected unopposed as the new Labor leader after contender Chris Bowen pulled out of the race.
But Queenslander Jim Chalmers is still considering whether to throw his hat in the ring.
Mr Bowen's decision to withdraw a day after announcing his tilt came as left faction senator Penny Wong appeared concerned about reports interim leader Bill Shorten, from the right, was actively trying to prevent Mr Albanese from becoming leader.
"I would be surprised if that were occurring," she told reporters in Adelaide
"It wouldn't be consistent with the role of a former leader or current interim leader and it would undermine the unity that Bill has been such an important part in rebuilding."
Mr Bowen withdrew on Wednesday afternoon once it became clear Mr Albanese had solid grassroots support.
The shadow treasurer insists he would have secured support from the majority of the Labor caucus, but concedes Mr Albanese would have won a vote of rank and file members "by a good margin".
"I have reached the view that it would be unlikely for me to win the ballot," Mr Bowen said.
"So ... not thinking it's really viable for me to win, it wouldn't be fair to put the party through the cost, the process and the delay for the start of a new leader."
Mr Bowen's withdrawal opened the door to another contender such as Mr Chalmers, who is also from the party's right, to take on the frontrunner from its left.
Mr Chalmers, who has been in parliament since 2013 as the member for the Brisbane seat of Rankin, is weighing up his next steps.
"I feel for Chris and I know it would've been hard for him to pull out," he said.
"I'm being encouraged to nominate for leader and I'll now consider my options overnight. Labor needs to rebuild, refresh and renew and I want to play a prominent role in that. What role is to be determined."
The Labor national executive met on Wednesday night to map out the leadership process, with nominations to open on Thursday and close on Monday.
If Mr Albanese is not the only candidate, ALP members will vote on their preferred leader in a postal ballot between May 31 and June 27.
The Labor caucus would then meet and cast their votes on July 1, with both the rank-and-file and parliamentary vote holding equal weight.
Mr Albanese believes the majority of his caucus colleagues are backing him, putting him in a good position to ward off challengers.
"I am confident, but not complacent, about being able to succeed if another candidate comes forward," he told reporters in Sydney.
"If they do, as is their right, we will have a respectful debate."
About 18 caucus members have so far come out in support of Mr Albanese, from across the party's left and right factions.
Mr Albanese won the grass roots support but lost the caucus vote in the 2013 leadership battle with Mr Shorten.
The process was set up by Kevin Rudd to end the "revolving door" of leadership.
Australian Associated Press