The EU will delay its decision on the length of the Brexit extension until next Monday or Tuesday after France piled pressure on MPs ahead of a vote on Boris Johnson’s demand for a pre-Christmas general election.

During a meeting of EU diplomats, the French ambassador stood alone in arguing that it was not the right time to agree a three-month delay, in a move that will be welcomed in Downing Street.

Only after the vote on Monday should the EU decide to “go short, to push for ratification, or long to accommodate a general election”, the ambassador told the other member states, according to a diplomatic note.

Sources close to the French president, Emmanuel Macron, later claimed an extension was “not a given” and needed to be justified. “But we have nothing of the sort so far”, the source said. “Pressure must be maintained.”

The prevarication in Brussels, and Macron’s swing behind Johnson’s strategy for getting a deal passed, will leave the issue of an extension in doubt with as little as 48 hours to go before the UK is due to leave.

Johnson has said he will give MPs until 6 November for further scrutiny of the withdrawal agreement bill if Labour accedes to his request for a general election on 12 December.

EU sources said that the chances of leaders being called to a last-minute summit to decide on an extension had risen. “It has not been ruled out at all,” a source said.

The 26 other member states are understood to have argued that France was playing a dangerous game by “playing ping-pong with the UK and reacting to every twist and turn”. “Let’s take a step back,” one diplomat said.

The delay is politically difficult for Jeremy Corbyn, who had said Labour would only vote in favour of a general election if the EU confirmed it would grant an extension to 31 January, taking a no-deal Brexit off the table.

The prime minister responded to the latest developments by calling for the Labour leader to “man up”.

After the two-hour meeting in Brussels on Friday, the EU’s chief negotiator, Michel Barnier, had conceded that an “excellent” discussion had concluded without any clear way forward. “No decision,” he said.

An EU source said of the meeting of EU27 ambassadors: “There was full agreement on the need for an extension. There was full agreement to reach a unanimous, consensual EU27 decision. And there was full agreement to aim to take the decision by written procedure … Work will continue over the weekend.”

The diplomatic source added that EU27 diplomats were “expected to meet early next week to finalise an agreement” and that the president of the European council, Donald Tusk, had “no intention” of calling a summit.

A majority of member states want to accept the terms of an extension reluctantly requested by Johnson, under which Brexit could be delayed until 31 January, but with the opportunity to leave earlier if the withdrawal agreement was ratified in Westminster and by the European parliament.

Those terms had been due to be signed off on Friday. “There is one country standing in the way – France,” a diplomat said. “Everyone is very frustrated. They were told that a short extension ran the risk of an accidental no-deal Brexit.”

“It is the French, always the French,” said a second senior diplomat. “And they never back down.”

Sources suggested that Macron, who described Johnson as having “strategic vision” at a recent summit, was keen to appear helpful to Downing Street by keeping the pressure on MPs.

As a result, if there is no general election, there remains the possibility that the EU will offer a shorter delay, to mid or late November, merely to allow time for ratification, although sources suggested this remained unlikely. “We agreed we all want to avoid a no deal – and a short extension will just raise the possibility,” said an EU source.

By meddling with the terms of the extension request laid out in the Benn act, the prime minister would also be placed under a different set of obligations. If the three-month extension to 31 January is offered, Johnson will have to agree to it. A different formulation would require parliament to pass a motion endorsing the extension request. Johnson would then need to formally agree to it with the EU by 30 October or within 48 hours, depending on which is earlier.