It's understood EU leaders are "very unlikely" to make a final decision on a Brexit delay before Tuesday.
They've agreed, in principle, to grant the UK an extension -- but are yet to settle on the length.
British MPs are expected to vote on Monday on whether to call a general election in December.
It was thought they would decide by Tuesday - two days before the latest official leaving date - but this is now looking unlikely, meaning Boris Johnson will be unable to fulfil his promise of leaving on 31 October "do or die".
Weekend talks by the 27 leaders are likely to be influenced by a leaked document, seen by the Financial Times, that indicates the British government may want to diverge away from the bloc's rules on workers' rights and environmental protections after Brexit.
There are fears by some EU nations, especially Germany, that Mr. Johnson is preparing to reform Britain into "Singapore-on-Thames" - a low-tax, lightly regulated economy on the edge of Europe - once it has left.