Labor says it will not stand a candidate in the by-election for former West Australian treasurer Troy Buswell's electorate of Vasse.

The by-election for what is widely considered to be a safe Liberal seat will most likely be held before early November, according to Speaker Michael Sutherland.

It comes after Mr Buswell's resignation from politics last week.

Labor leader Mark McGowan said rather than putting up a candidate, the party would instead watch the Liberal and National parties "tear each other apart".

"We'll leave the Liberal and National parties to tear each other apart, and you won't need tickets to see that event," he said.

"This will be an opportunity for them to rip at each other over that electorate, and I think that will be a good opportunity for the public of Western Australia to see what is going on inside the ranks of the Government."

Mr McGowan said the party would instead divert its resources towards the 2017 state election.

Premier Colin Barnett seized on the comments during Question Time, telling Parliament the only reason Labor was not running is because it would lose.

"Why did you pull out of the Vasse by-election?" he asked.

"Because no-one there knows who the Labor Party is! And they don't even know who you are. That's the reason you pulled out. That's the reason, you would have come fourth.

"Imagine that, the State Opposition comes in a close fourth in a field of four, that would have been the result."

Mr Buswell held the blue ribbon seat with a 21 per cent margin, and has remained popular despite a series of scandals.

The Liberal Party says it will endorse a local for the seat, rather than parachuting in an outsider, while the Nationals will announce their candidate in two weeks.

The parliamentary Speaker said the election would likely be held within the next two months.

"I think we have to take into consideration school holidays, and the parties have to get their houses in order and nominate candidates," Mr Sutherland said.

"So I would assume towards the end of October or early November, but no date's been set yet."