Outspoken MP Craig Kelly abruptly left the Liberals after being reprimanded by the Prime Minister for derailing the government's vaccine rollout by speaking in favour of alternative COVID-19 treatments.

Mr Joyce wasted no time making his pitch to the outspoken MP and was caught in his office just minutes after he officially became an independent.

"I would love him to be in the National party but that's really a decision for Craig," Mr Joyce said.

"My job first and foremost is to give him space and be his mate, but if someone wants to join the Nationals, I tell you what, I'm the last person to talk them out of it.

"Any time to make the National party bigger, I'm going to grab it with both hands, that's what you do."

It has been alleged Mr Joyce has 10 of the 21 Nationals in his camp, including all the party's senators and MPs Llew O'Brien, George Christensen, Ken O'Dowd and David Gillespie.

Mr Kelly joining the party would have given Mr Joyce 50 per cent of the party room vote, enough to challenge for the leadership with a chance of swaying an MP loyal to leader Michael McCormack.

Senator Bridget McKenzie said "the door was always open" for Mr Kelly, who had joined the Nationals to fight on a number of fronts over the years.

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"There is a lot of synergy with Craig's view of the world and what we come to Canberra to fight for," she said.

Mr McCormack refused to be drawn on whether he thought Mr Kelly would be a good fit for the party.

Mr Kelly has stated he would not join the Nationals or any other party - for the moment - and would stand as an independent at the next election.

"I'm not sure whether a pair of RM Williams and a big Akubra and a Driza-Bone will necessarily work in [my electorate] Sutherland," Mr Kelly said.

But Mr Kelly's declaration hasn't slowed the leadership speculation.

Nationals Senator Matt Canavan - a long-time Joyce supporter who lost his ministerial portfolio at the 2020 spill - took the opportunity to take a swipe at Mr McCormack leadership style.

"Of course I support the leader, but I have said consistently I like to see the National Party take a more assertive and aggressive approach on issues," Senator Canavan said.

"I have consistently said I like to see us take a more assertive role on issues. I'd like to see Michael [McCormack] step up to the plate and take up these issues. That's what I'd like to see."

When asked if Mr Joyce would do a better job as leader if he put his hand up, Senator Canavan responded: "He hasn't done that".

Prime Minister Scott Morrison - who intervened to save Mr Kelly before the last federal election when he faced a preselection challenge - was asked if he was worried the MP would join the Nationals.

He replied "no, I don't, but that's really a matter for others".

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