David Cameron has refused to take part in the debates unless the Green Party is included.
Mr Clegg told the BBC he thought the debates would go ahead, but suggested the proposed format needed to change.
Earlier this week Mr Clegg, the deputy prime minister, said the broadcasters should grow a "backbone" and push ahead without Mr Cameron if necessary.
The plans put forward by the BBC, Sky News, ITV and Channel 4 in October would include the Conservatives, Labour, Liberal Democrats and UKIP.
One would feature a head-to-head between Mr Cameron and Labour leader Ed Miliband, another would also include Mr Clegg, and the third would feature the leaders of the Tories, Labour, Lib Dems and UKIP.
The suggested schedule is for debates on 2 April, 16 April and 30 April, ahead of the UK-wide poll on 7 May.
Mr Cameron has said all "national parties" must be represented at the live televised pre-election debates - which were first introduced for the 2010 general election.
Labour leader Ed Miliband has said it was a "pathetic excuse" to avoid the debates, but Mr Cameron said Mr Miliband was "chickening" out of debating the Greens.
On the BBC's Andrew Marr show on Sunday, Mr Clegg said Labour and the Conservatives were using the Greens as an "alibi" to block the debates.
"They want to put the genie back in the bottle. They want to run things as they've done before. I think it's too late," he said.
Mr Clegg, Mr Miliband and UKIP leader Nigel Farage have written to the prime minister saying it would be "unacceptable" for him not to appear.
In separate but identical letters sent earlier this week they urged the broadcasters to press ahead with the debate before the general election.
Mr Clegg said: "The broadcasters need to come forward with other proposals because clearly the current one - which I'm not wildly happy about because it excludes me as a leader of a governing party - so they need to come forward with a proposal.
"I'll get my soapbox out any day of the week."
Asked by Green Party in England and Wales leader Natalie Bennett - who was also on the programme - whether he would lobby for her party to be included, Mr Clegg said it was not for politicians to tell the broadcasters what to do.
Ms Bennett says the polls and public opinion support the argument for the Greens to be included.

The "iPitch" at the Stobart Stadium was criticised by former Warrington full-back Richie Mathers, who posted images of grazes to his body on Twitter.
He described the surface, on which his side won 32-14, as an "absolute joke".
But Widnes claim that Mathers' injuries are more likely the result of the icy conditions the match was played in.
The club's chief executive, Julie Gaskell, stated: "We had four games on the pitch this weekend and you have to bear in mind the extreme weather. On Friday night, it went down to minus seven.
We are happy for Widnes to continue using the iPitch
"The injuries are consistent with those on any surface in those temperatures. We noted there were similar injuries from the game at Salford on Saturday.
"Our players have been training on a similar surface for the last nine months and there have been no issues. I am sure any problems would have shown up.
"We have also had five-a-side football and boys and girls tag rugby on the pitch over the last four weeks and again we have had no reported injuries."
The Rugby Football League say their match commissioner had no concerns about the surface, which is the first artificial pitch ever to be used in the sport.
"We are happy for Widnes to continue using the iPitch," said RFL spokesman John Ledger.
"The indications are that it posed no more danger to players than on any other surface over the weekend. We believe the extreme weather may have been an issue."
Lib Dem leader Nick Clegg has said the broadcasters should come up with "other proposals" for the TV election debates.
[NEXT_CONCEPT]
Widnes have rejected concerns raised about the safety of their artificial pitch following Friday night's Super League opener against Wakefield.