Boris Johnson has signalled his intention to appear in a BBC debate on the Tory leadership – but not one on Channel 4.
But his absence from the first televised event leaves the prospect of Channel 4 empty-chairing the aspiring prime minister.
Mr Johnson has said that there would be too many people involved in the Channel 4 broadcast on Sunday – suggesting it would be too "cacophonous".
Six hopefuls remain in the Tory leadership race after Health Secretary Matt Hancock withdrew.
By the time the BBC debate takes place on Tuesday evening, the field will have narrowed further following a second leadership contest ballot.
Mr Johnson told The World At One: "I think it is important that we have a sensible grown-up debate.
"My own observation is that in the past when you've had loads of candidates, it can be slightly cacophonous and I think the public have had quite a lot of blue on blue action frankly over the last three years.
"We don't necessarily need a lot more of that and so what I think the best solution would be, would be to have a debate on what we all have to offer the country.
"And the best time to do that, I think, would be after the second ballot on Tuesday, and the best forum is the proposed BBC debate.
"I think that's a good idea."
He told the BBC that he is "more than happy" to take part in the BBC One leadership debate.
Channel 4 is broadcasting the first live leadership debate between the main candidates vying to become the next prime minister.
Its 90-minute programme will be hosted by Channel 4 News presenter Krishnan Guru-Murthy, in front of a live studio audience drawn from across the UK.
Mr Guru-Murthy called on Mr Johnson to appear on Live: Britain's Next PM – The C4 Debate, saying that the BBC event would have "fewer rivals".
"BBC show is very different with fewer rivals after second round of voting and no live studio audience," he said on Twitter.
"Is possible, for instance, he won't face biggest critic Rory Stewart or Brexiteer rival Dominic Raab."
Channel 4 director of programmes Ian Katz has said: "The next British prime minister will be chosen by 330 MPs and 120,000 Tory party members – just 0.2% of the population – so it's vital that they are properly tested before the wider electorate.
"There has been a dismaying trend in recent years towards major politicians avoiding taking part in televised debates, but we're hopeful that this will mark a return to healthy public scrutiny of candidates for our highest office."
A Channel 4 spokesman said: "We are disappointed that Mr Johnson will not be taking part in the debate to face members of the public for full scrutiny alongside the other candidates.
"There will be a lectern available if he changes his mind."
On the BBC, Emily Maitlis will put the "future UK prime minister to the test".
The public will be able to question the leadership hopefuls, live on air, from BBC studios across the UK.
The programme, Our Next Prime Minister, will air just two hours after the second ballot.
Members of the public will be invited to "pose questions on any topic in the prime minister's in-tray".
BBC executive producer Jonathan Munro said: "This is a programme which allows the BBC's audiences to set the agenda, and ask the questions which are at the forefront of their minds.
"It'll be broadcast at a key moment in the process of narrowing down the field of candidates in the race for Downing Street."