Conservative leadership contender Mark Harper said he would "bust a gut" to get a new deal with the EU.
The former chief whip said the only way to win the support of fellow Tories was to show "you've tried and failed" in Brexit negotiations.
"You have got to show that you've busted a gut to get a new deal," he told talkRADIO's Julia Hartley-Brewer.
"It's only if you've really shown you've tried and failed will those Conservative MPs be prepared to contemplate it, and it is only then that you can leave without one."
However, he said that promising a "deal or no deal" exit in the autumn and not keeping to it could "energise the Brexit Party".
"We are only going to be able to beat the Brexit Party if we deliver Brexit, not just talk about it," he added.
"That means you have to have a credible plan. I don't think it's credible to say you can leave on October 31 deal or no deal."
He continued: "If we make another promise to leave on October 31 and it's not kept, then I think that will energise the Brexit Party rather than destroying it."
A Labour motion to block a no-deal Brexit will be voted on today in the Commons, but Mr Harper said he would be voting against it.
"We're going to see an attempt today by Parliament and I don't know whether it's going to be successful. I will be voting against the Labour motion and I will be voting to keep no deal on the table," he said.
"What that proves is that Parliament, if there is a majority that wishes to stop Brexit, is able to do so if it wants."
Tomorrow, the 10 leadership candidates will face another round of voting, in which they must secure the support of at least 17 MPs to stay in the race.
"I'm in this to win this," Mr Harper added.
"I am confident, not complacent, that I can clear the hurdle on Thursday."