Leadership pressure on Barnaby Joyce has escalated again after the man touted as his main rival, Michael McCormack, repeatedly refused to rule out a challenge or pledge his support for the Deputy Prime Minister in an awkward live TV interview.

Mr McCormack would only acknowledge Mr Joyce remains leader "at the moment" and that "at the moment" no challenge was under way.

It followed his comments to Fairfax Media on Saturday in which he also refused to rule out a challenge and said a leadership showdown "depends on what happens" this week as Nationals MPs "take a temperature reading" among constituents and branch members about Mr Joyce, his affair with a former staffer and his leadership.