Deputy Prime Minister Warren Truss says the Nationals' coalition agreement can't be guaranteed if the Liberals change leaders.
Mr Truss is chairing the Nationals' first party room meeting of the year in the Victorian regional centre of Wodonga.
Some Liberal MPs are agitating for a leadership spill at the party's meeting in Canberra next Tuesday.
But neither of the potential contenders, Malcolm Turnbull and Julie Bishop, have declared their hands.
Mr Truss said the coalition agreement, signed in the wake of the September 2013 election victory, was a deal between him as Nationals leader and Mr Abbott as Liberal leader.
"The coalition agreement is between Tony Abbott and me," the Nationals leader told reporters on Thursday.
"And that's an agreement we submitted to the governor-general so that she was able to commission the government.
"So that is an agreement between the Nationals and the Liberals but particularly an agreement between Tony Abbott as leader of the Liberal Party and me as leader of the Nationals."
A revised agreement would have to be signed if the Liberal leadership changed.
"At this stage I don't think that is likely to be an issue," Mr Truss said.
"I'm happy to be working with Mr Abbott, I think he's doing a good job."
But he added the Liberal leadership issue needed to be settled quickly.
Nationals MPs have previously expressed concern with Mr Turnbull over his support for an emissions trading scheme.
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