Former deputy prime minister Barnaby Joyce has urged Prime Minister Malcolm Turnbull to do the “honourable thing” and step down if he cannot revive his political fortunes by the end of the year, in an early move within the Coalition to set a timetable to decide the leadership.

Mr Joyce named Christmas as a likely deadline to decide Mr Turnbull's fate, breaking ranks with fellow MPs who are defending the Prime Minister in public after the Coalition suffered another loss in the polls.

The comments are certain to inflame the Coalition’s internal debate after Mr Turnbull lost his 30th Newspoll survey in a row, days after also losing a Fairfax/Ipsos poll showing the Coalition was trailing Labor by 48 to 52 per cent in two-party terms.

Barnaby Joyce and Malcolm Turnbull in Parliament in February. Credit:Alex Ellinghausen

Mr Joyce said “Malcolm’s not a fool” and knew he would have to stand aside by the end of the year if the government did not stage a comeback.