Mrs May has struggled to get enough support for her deal, with more than 100 Tories and the vast majority of MPs from other parties said to be planning to vote against it.
Downing Street said Mrs May would be making a Commons statement on Brexit at 3.30pm, when she is expected to confirm the announcement.
The prime minister is "not totally comfortable" with the backstop, Hunt said.
The government is widely expected to lose the vote, with Labour, the Liberal Democrats, the DUP, the SNP and dozens of Conservative MPs saying they can not support the deal.
Some pro-EU lawmakers have also expressed support for a second referendum on European Union membership, or "a people's vote".
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Mrs May has reportedly held a crisis call with ministers ahead of the key vote tomorrow which could make or break Mrs May's future as PM.
"It would mean grave uncertainty for the nation with a very real risk of no Brexit", she told the Mail on Sunday.
Her proposal needs the backing of 320 MPs, more than half of the 639 MPs that vote in Parliament, to pass.
The warning came two days ahead of a crucial Brexit vote in the House of Commons.
It is unclear what would happen if the deal fails, but it could put Britain's Brexit plans in jeopardy and May's job on the line.
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You can't please everybody. "I think there's little things that might just get inside his mind", he said. Spearhead Ishant Sharma averages 62 over 10 Tests in Australia and took 1-73 in Sydney .
"What has happened in the last week is that any prospect of no deal has been removed by amendments allowing Parliament to take control, while we now all know beyond any doubt that we can stay in the European Union - it's not too late".
It comes as the European Court of Justice is expected to deliver its final ruling on whether the United Kingdom can unilaterally decide to halt Brexit this morning.
But her hopes have already been dashed by the European commission, whose deputy chief spokesperson said: "We will not renegotiate the deal that is on the table right now". Its most controversial propositions concern the future of EU citizens in the UK and British citizens residing in the EU-27, the framework of bilateral EU-UK trade relations, and the "regulatory regime proposed for Northern Ireland".
But speaking on the BBC's The Andrew Marr Show, Barclay said the vote would take place on schedule.
Rudd told The Times newspaper in an interview her own preferred option, if May's deal failed, was the "Norway Plus" model, adding it "seems plausible not just in terms of the country but in terms of where the MPs are".
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Search and rescue efforts were ongoing, United States and Japanese officials said. It was not clear how many crew members were on each of the planes.
Meanwhile Alan Duncan, foreign minister, said that some Tory MPs were planning to vote against Mrs May's deal to further their own political ambitions, calling such behaviour "contemptible".