Labor’s candidate for the Brisbane seat vacated by government MP Chris Davis has begun campaigning less than 24 hours after his predecessor’s departure.

Labor’s candidate for the Brisbane seat vacated by maverick former government MP Chris Davis has vowed to be a thorn in Premier Campbell Newman’s side if he’s elected.

But maxillofacial surgeon Dr Anthony Lynham is playing down his chances of winning Stafford, an electorate devoid of representation after Dr Davis quit parliament on Friday.

His dramatic departure means the LNP is facing a by-election battle just three months after suffering a 17 per cent swing against it in the Redcliffe poll.

However, Dr Lynham says winning Stafford won’t be a cakewalk.

“We are not taking anything for granted, we have to earn it,” he told AAP while campaigning on Saturday.

As an anti-violence campaigner, Dr Lynham says he’s already taken Mr Newman to task and will up the ante if he enters parliament.

“I have a proven track record of standing up to Newman,” he said.

“The people of Stafford need someone desperately to stand up to Newman on health and education.

“I will be a thorn in his side.”

Opposition Leader Annastacia Palaszczuk has already promised to give Dr Lynham a senior position if he’s elected, but she’s also downplayed her party’s chances of regaining Stafford, which the LNP holds by a 7.1 per cent margin.

Ms Palaszczuk says Dr Davis’ resignation was a vote of no confidence in Mr Newman’s leadership and has called on the premier to immediately announce a by-election date.

Dr Davis said he was partly demoted because he raised concerns with the premier about looming changes to political donations.

He was sacked as assistant health minister a week earlier after clashing with colleagues over the proposed individual contracts and changes to the state’s corruption watchdog.

At the time of his resignation, Dr Davis released polling showing most voters in his Stafford electorate backed him and believed he had been unfairly treated.

Treasurer Tim Nicholls said Dr Davis’ exit was disappointing and came after colleagues had urged him to stay with the party and effect change within government.

Mr Nicholls said the government expected a tough fight at the by-election.

“The premier is getting advice about the timing of calling a by-election and I’m sure he’ll make an announcement in the near future,” he told reporters.

Brisbane Central MP Robert Cavallucci would represent the interests of Stafford in the interim, he said.