The PM has said he will give MPs more time to debate his Brexit deal, if they agree to a 12 December election.
Boris Johnson told the BBC he expected the EU to grant an extension to his 31 October deadline, even though he "really" did not want one.
But Jeremy Corbyn said he would not support an election until a no-deal Brexit is "off the table".
EU leaders could give their verdict on delaying Brexit for up to three months on Friday.
Commons leader Jacob Rees-Mogg told MPs the government would on Monday table a motion calling for a general election.
Under the 2011 Fixed-Term Parliament Act, two-thirds of MPs must vote for a general election before one can be held.
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