Malcolm Turnbull is expected to name Greg Hunt as the new health minister in the wake of Sussan Ley's resignation.
The prime minister is also tipped to reveal on Wednesday that Cabinet Secretary Arthur Sinodinos will take over Mr Hunt's role as industry minister.
However a wider ministerial reshuffle is off the agenda.
"There is one vacancy," Mr Turnbull told 4BC radio on Tuesday.
Amid speculation Senator Sinodinos would take on the health role, Labor has stepped up its attack on the former chief of staff to John Howard.
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Labor leader Bill Shorten told reporters in Sydney on Tuesday it would be wrong to "recycle" Senator Sinodinos while there were questions arising from a NSW Independent Commission Against Corruption inquiry.
"The only reason Malcolm Turnbull is having a reshuffle is because one of his government ministers was mistreating the expenses system and making Australians really angry at all politicians," Mr Shorten said.
"What Malcolm Turnbull should be doing today is not recycling the dodgy Senator Sinodinos ... he should, instead, be focusing on policies which help promote and maintain Australian jobs."
Mr Turnbull said Mr Shorten was seeking to distract from the failings of his own team.
The prime minister has declined to release the advice he received from an independent review of Ms Ley's travel expenses, which included a trip to the Gold Coast during which she bought an apartment.
However an independent watchdog will oversee politicians' expenses with new rules, including monthly declarations, being brought in mid-year.
Mr Hunt, who hails from Victoria's Mornington Peninsula, was environment minister from September 2013 before taking on the industry, innovation and science portfolio after last year's election.
As industry minister he took a close interest in biomedical research, nuclear medicine and medical technology.
