He said it was unlikely the draft deal, which was published on Wednesday, would secure enough parliamentary support in a crunch vote billed for December. In a BBC radio interview on Sunday, he didn't sound like someone on the brink of unleashing political chaos.
More than 20 lawmakers have said publicly that they have submitted a letter, but others are expected to have done so confidentially.
He described Mrs May's plans for a temporary customs arrangement to prevent a hard border in Northern Ireland as a "sticking plaster" which will "prolong the uncertainty and put jobs and prosperity at risk".
May said she was headed to Brussels for talks with European Commission President Jean-Claude Juncker before EU leaders gather on November 25 to finalize the draft Brexit agreement.
The Brexiteer Commons leader Andrea Leadsom said there is still time for "more to be done" on the Brexit deal.
The EU nations and Britain are still negotiating the outline text of a future relationship which should be ready in the coming weeks.
He warned MPs against submitting no confidence letters to Sir Graham Brady, chairman of the backbench 1922 Committee, saying: "It's a total distraction from what we need to do, we need to get Brexit over the line, we need to support our Prime Minister".
The 27 other EU nations have started examining the 585-page draft withdrawal plan - this text outlines how the United Kingdom will leave the European Union and is the sole reason why several United Kingdom politicians have turned their back on the prime minister in the last 48 hours.
"The focus this week will be on the future relationship".
British newspapers reported that five senior pro-Brexit ministers were working to pressure May to change the deal, but May said she saw no alternative plan on the table. "I don't think you call a referendum and then say you don't like the result and go away from it, you've got to understand why people voted and negotiate the best deal you can", he added.
Brexit secretary Dominic Raab resigned in protest against the deal last Thursday and the rightwing of May's Conservative Party has been calling for her to resign and threatening an internal leadership challenge.
"If you're signed up in government and you're in the Cabinet, normally I would expect you to be able to share the document and to know the direction of travel of this negotiation".
Many business chiefs and investors fear politics could torpedo an agreement, thrusting the economy into a no-deal void that they say would weaken the West, spook financial markets and silt up the arteries of trade. She said: "It will no longer be the case that European Union nationals, regardless of the skills or experience they have to offer, can jump the queue ahead of engineers from Sydney or software developers from Delhi".
Asked about calls for a second referendum Corbyn said: "It's an option for the future but it's not an option for today, if there was a referendum tomorrow what's it going to be on, what's the question going to be?"