Barnaby Joyce says if Malcolm Turnbull can't arrest the government's polling woes by the end of the year, he should consider stepping down as prime minister.
The coalition lost a 30th Newspoll in a row on Monday, a mark Mr Turnbull used as a reason to dump Tony Abbott.
Former Nationals leader Mr Joyce - who doesn't have a say on the Liberal leadership - wants to wait until after the budget to make a "fair judgment" on Mr Turnbull's position.
Mr Joyce said if credible polling continued to be poor deeper into the year, the prime minister should look at making way for an alternative leader.
"You have an obligation not to drive your party or the government off a cliff," Mr Joyce told Sky News.
"Nobody wants to go to a federal election which you know you're going to lose. It's like playing in the losing grand final - no one wants to play in the losing side.
"You have an obligation to all around you that if you honestly believe that is the case, then you must do something about it and do the honourable thing and start grooming an alternative."
Mr Joyce insists the government is a "long, long way" from getting to the point where the government should look at switching leaders.
His comments on Mr Turnbull's future come months after the two men engaged in a public stoush during the fall out from Mr Joyce's affair with a staffer.
A furious Mr Joyce blasted Mr Turnbull for what he perceived as a request to stand down from his role as deputy prime minister.
"In regards to the National party, there is nothing we dislike more than implied intervention into the party processes of the National party," Mr Joyce said in February.