Mary Wooldridge.

Mary Wooldridge. Photo: Michael Clayton-Jones

Victorian Premier Denis Napthine's election campaign has been dealt an embarrassing blow, with senior minister Mary Wooldridge losing preselection for the state seat of Kew.

Dr Napthine and his government had been vocal supporters of Ms Wooldridge after her seat of Doncaster was abolished in last year's redistribution.

Last week Dr Napthine wrote to every local branch member pleading with them to vote for cabinet Ms Wooldridge, warning "I need her skills and expertise by my side".

Dr Napthine's letter warned that the government is facing a tough election at the end of the year, making it "vital" that Ms Wooldridge is selected for the seat.

But on Sunday Kew members voted strongly in favour of Tim Smith, a former mayor in Stonnington. Mr Smith was backed by several former federal ministers including Richard Alston.

Ms Wooldridge was seen by many in the state parliamentary team as critical to their chances of re-election in November.

The Age/Neilsen poll this weekend found that Dr Napthine's government was trailing the Labor Opposition 47-53 on a two party preferred basis.

Emerging from the vote Mr Smith told the media he was humbled to be selected but would not take any questions.

"I'm truly humbled. I've huge respect for Mary Wooldridge and I wish her all the very best," he said.

Ms Wooldrige, who is Community Services Minister, said she respected the decision and would now talk to her husband about her political future.

"Obviously I'm disappointed, but it's an important part of a democracy of our party," she said.

Dr Napthine said Ms Wooldridge would remain in his cabinet. He said the Liberal party had an open democratic preselection process involving two quality candidates.

"I'll be certainly talking to Mary Wooldridge and making sure we do everything we can to keep Mary Wooldridge in my team and in the parliament," he said.

"I'll be encouraging Mary Wooldridge to continue her state parliamentary career because I believe she has enormous talent, enormous skills and a lot to offer."

As late as last Thursday Dr Napthine had been adamant that Ms Wooldridge would win the seat and on Sunday he said he did not regret his public support.