The Nationals are hoping newly-elected West Australian MP Tony Crook will join their party room at some stage during the new federal parliament.
Mr Crook, who ousted veteran Liberal MP Wilson Tuuckey in the seat of O'Connor at the August 21 election, has confirmed he plans to sit on the crossbench in the 150-seat lower house.
His decision means there will be six MPs, including an Australian Greens member, on the crossbench.
Parliamentary secretary Kate Lundy said the decision was a "real blow" to the opposition.
"I think that sends a pretty strong signal about the level of discomfort at the way (Opposition Leader) Tony Abbott is taking his approach to this new minority parliament."The announcement from Crook came shortly before MPs returned to Canberra on Monday, amid the continuing row over the Speaker.
Mr Abbott said it was the coalition's intention to make the parliament work under Labor's minority government, but it "should be working in the national interest, not just the interests of the Labor Party."
Nats want Crook as 'part of the team'
Nationals leader Warren Truss said Mr Crook had told him he was honouring an election campaign commitment not to sit with the coalition.
"I think he could have achieved far more for his constituency by being part of the team than he'll be able to do alone," he told ABC Television on Monday.
"But on the other hand we recognise the commitment he made."
Nationals MP Bruce Scott hopes his party and Mr Crook can work together.
"At some time in the future he may see that it's important to be part of a team rather than an individual," he told reporters in Canberra on Monday.
"He'd be much better in a team at the end of the day."
Liberal senator Mitch Fifield said the coalition was unperturbed by Mr Crook's decision.
"We all know the West Australian National party marches to the beat of a different drum," he told Sky News, adding it was a "proudly independent" party.
"We respect that, but on the centre-right we're going to be pretty ecumenical in our approach and I'm sure we'll work well with Mr Crook."
