West Australian Opposition Leader Mike Nahan has again urged Colin Barnett to quit politics after the former Liberal premier criticised his own cabinet.

Mr Barnett recently told The West Australian newspaper his second-term cabinet was not as strong as his first.

Dr Nahan said he disagreed with his former leader and believed Mr Barnett should resign from parliament.

"I would like to see refreshment in the seat of Cottesloe," Dr Nahan told reporters on Thursday.

But Mr Barnett said he had given an honest assessment of his government.

"It's no disrespect to any of the ministers in the second term, but I think we lost five very good ministers from the first term and that has an impact. It's as simple as that," he told reporters.

Mr Barnett maintains he will decide his future at the end of the year.

WA Premier Mark McGowan said it appeared the Liberal party was at war.

"What Mr Barnett said about his own cabinet, I think, was right. They weren't very good and the people recognised that," he told reporters.

"If Mr Barnett has no faith in the Liberal party, why should anyone else?"

After the Liberals' crushing election defeat in March, Dr Nahan said he believed Mr Barnett should retire "sooner rather than later", but then backtracked when the former premier indicated he wanted to stay on.