The French leader said the EU did not know how the incoming British prime minister would act in relation to the ongoing Brexit crisis.
“I hope from my side that we finish before [31 October],” Mr Macron said at a press conference at the end of the latest EU summit.
“We shouldn’t be scared of the worst-case scenario, which is always a possible option, and at the end of the day [it] will be the responsibility of the British ... because at the end of the day until the last second the British government has the possibility to withdraw Article 50 and decide not to leave,” he said.
The UK is currently scheduled to leave the EU on 31 October but parliament is yet to approve the deal agreed between Theresa May’s government and the EU.
EU figures have already granted the UK one Article 50 extension, from 31 March to 31 October. Mr Macron said new elements would be needed to justify a second delay, if an agreement had not been reached by Halloween.
Ms May is due to step down later this month and will be replaced by either Boris Johnson or Jeremy Hunt. Both candidates have refused to rule out crashing out of Europe.
Mr Hunt, who is considered the more moderate of the pair, has unveiled a 10-point plan for a no-deal outcome. The foreign secretary admitted on Tuesday that a no-deal Brexit could inflict as much damage as the 2008 financial crash.
But he vowed to take the UK out of Europe without a deal if necessary. “This is a country where we do what the people tell us, so we have to deliver Brexit,” he said.
“We have to make it a success and part of the way we’ll make it a success, first of all, is preparing for a no-deal Brexit.”
Mr Johnson, widely considered the front runner to replace Ms May, has pledged to take the UK out of the EU on 31 October “do or die”.