Boris Johnson is to meet Emmanuel Macron today, hours after the French president seemed to downplay hopes of solving the Irish backstop problem.
On Wednesday, German Chancellor Angela Merkel suggested a solution to the backstop – a key Brexit sticking point – might be achievable within 30 days.
The PM said he was “more than happy” with that “blistering timetable”.
But later on Wednesday, Mr Macron insisted reopening negotiations on the issue was “not an option”.
Mr Johnson has said that the backstop – which aims to prevent a hard Irish border after Brexit – must be ditched if a no-deal exit from the EU is to be avoided.
The EU has repeatedly said the withdrawal deal negotiated by former PM Theresa May, which includes the backstop, cannot be renegotiated.
But at a news conference in Berlin with Mr Johnson on Wednesday, Mrs Merkel indicated that an alternative might be possible, stressing that the onus was on the UK to find a workable plan.
“It was said we will probably find a solution in two years,” she said. “But we could also find one in the next 30 days, why not?”
A Downing Street spokesman described the meeting of the two leaders as “constructive”.
However, hours later, Mr Macron appeared to downplay the prospects of a breakthrough, telling reporters in Paris: “Renegotiation of the terms currently proposed by the British is not an option that exists, and that has always been made clear by [EU] President Tusk.”
BBC political correspondent Ben Wright said Mr Johnson was likely to get a “chillier reception” from Mr Macron, who sees Brexit as “contaminating the whole European project” and wants it over and done with.