Former Victorian premier Jeff Kennett says he will take the next 48 hours to consider a return to politics.

Speculation about a comeback by Mr Kennett has been heightened by the resignation of Victorian Liberal leader Robert Doyle.

Mr Kennett says he has not spoken to any of his former colleagues today because he has been involved in meetings all day.

But he says he has been approached about returning to the party.

"I have received over the last few months significant numbers of approaches from both political and non-political people," Mr Kennett said.

"Obviously, what happened today in terms of Robert's resignation, I think caught most by surprise.

"I don't mean to mislead anyone, be they community or party members.

"I will, however, use the next 48 hours to consult with my existing and former colleagues, with those whose advice I think highly of, and obviously my family."

Mr Kennett says he will not take a long time to make up his mind.

"I do not want the speculation to continue unnecessarily long," he said.

Kennett 'has numbers'

Federal Treasurer Peter Costello says Mr Kennett could replace Mr Doyle, even though Mr Kennett is no longer in Parliament.

"Jeff Kennett has the numbers, he can run presumably," he said.

"You could become the leader and contest the next election."

But Professor Brian Kosta, of Swinburne University, says he doubts the party could pick a leader who is not in the Parliament.

"I think it would be a very retrograde step and I don't think it would happen," he said.

"It would be politically suicide to have somebody from outside the party leading the party.

"We'd have a rendition of not the faceless men of the Labor Party in the 1960s but the faceless man of the Liberal Party in the 21st Century."

The Prime Minister John Howard has endorsed a possible return to politics by Mr Kennett.

Speaking in Sydney tonight Mr Howard said he never thought politics had ever left Jeff Kennett's blood.

"If he comes back then that will be a good thing for the Liberal Party in Victoria, but it's a matter for him and Felicity to decide and I'll leave it to them to make up their minds," he said.

Doyle's resignation

Mr Doyle's resignation today was a surprise to many Liberal MPs.

But he says he was not pushed out of the top job.

"I had to say I gave it my best shot, I am happy with that," he said.

The new Liberal leader will be elected on Monday.

Frontbenchers Terry Mulder and Ted Baillieu are considering standing.

The state's election will be held in November.