The Labour leader made the admission as Transport Secretary Chris Grayling denied there was a “void” in government over Brexit during an interview with Sky News.
MPs are due to return to Westminster on Monday – a day before they will vote on whether to pass or reject the prime minister’s divorce deal with Brussels.
Mr Corbyn was pressed repeatedly on the BBC’s Andrew Marr Show to name a date for when he would table a no confidence vote but refused to.
He said: “We will table a motion of no confidence in the government at a time of our choosing, but it’s going to be soon, don’t worry about it.”
Senior shadow cabinet ministers have also said it will come soon, with shadow justice secretary Richard Brugon telling Sky News on Thursday it will be “a matter of days at the most”.
Mr Corbyn also suggested he would extend Article 50 if a general election was called and he won the keys to Downing Street.
“Clearly there’s only a few weeks between that and the leave date, there would have to be time for those negotiations,” he said.
And he hinted at his opposition to another referendum, saying: “My own view is that I’d rather get a negotiated deal now, if we can, to stop the danger of a no-deal exit.”
Mr Grayling tried to woo Conservative MPs to back Mrs May’s deal, calling it a “sensible compromise”.
He told Sky News’ Sophy Ridge on Sunday: “It’s not giving everybody everything what they want, but it was never going to – this was a 52-48 result.”
Asked if he had got everything he wanted, the Brexiteer admitted: “Of course not.
“The prime minister herself has said this is not the perfect deal.
“But if you offered me this deal back in 2016 at the time of the referendum and you’d have said instead of staying in the EU you can have this, I’d have said thank you very much.”
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Mr Grayling also talked down reports of calling in military chiefs to help plan for a no-deal divorce, but admitted some Ministry of Defence staff were being seconded.
He was given a chink of hope by Labour MP John Mann, who also told Sky News he was likely to side with the government on Tuesday.
“A day is long time in politics so things can change but as it stands it is likely I will vote for the deal, yes,” he said.
The UK is due to leave the EU by default on 29 March.
More than 90 Conservative MPs said in December they would vote against Mrs May’s deal.