Mr Grayling, a prominent Leave campaigner, told the BBC's Andrew Marr Show that he believed pressure from EU-based farmers would ensure a deal is done.
However Chris Grayling, the Tory transport secretary, told the same programme that Mr McDonnell was "talking a lot of complete nonsense" and the UK's membership of the European Union would expire automatically in March 2019, and parliament couldn't stop it.
An amendment to the Brexit bill tabled by Tory former cabinet minister Dominic Grieve would decree that any final deal has to be approved by Parliament, giving MPs - most of whom supported Remain during the European Union (EU) referendum campaign previous year - the power to reject any agreement struck with Brussels by Prime Minister Theresa May.
He attacked the Government for being "more interested in negotiating to save the Tory party than in the interests of the country", adding: "It's a disgrace".
He called on ministers to publish legal advice about what they were obliged to pay the European Union in their so-called divorce bill, claiming that it was "perfectly reasonable" to do this.
Downing Street has said £250m will be spent this year on preparing for the UK's exit, including the possibility of it leaving without an official deal.
Mr McDonnell's comments came as it was reported a powerful group of MPs had drawn up a plan to block the United Kingdom government from proceeding with a no deal Brexit.
"John McDonnell was talking a lot of complete nonsense", Mr Grayling said. I think on a cross-party basis you'll see in the debates in the coming week...
The cross-party group - which includes prominent Conservative, Labour, Liberal Democrat, SNP, and Green MPs - seek to give Parliament the power to stop the United Kingdom leaving talks with Brussels without a deal, according to The Guardian, despite barely more than one in four Britons believing that "any deal is better than no deal".
He rejected suggestions that flights would be grounded - as one major airline has suggested - in the event of a no-deal Brexit, insisting "people will be able to carry on making their bookings".
Himachal Pradesh: Anil Sharma to join BJP
Anil Sharma said, he will strive to fulfill the dreams of Prime Minister Narendra Modi by joining the BJP. He also claimed to have not been included in any of the committees in the run-up to the Assembly polls.