David Cameron is to visit Paris on Monday evening for talks with President Francois Hollande ahead of a crunch EU summit on Thursday.
Securing French agreement to a package of EU reforms will be crucial if a deal is to be reached in Brussels at the end of this week, clearing the way for a referendum on UK membership before the summer.
The Prime Minister must win over Mr Hollande on proposals for protections for non-eurozone states, which have caused consternation in Paris.
Mr Cameron is insisting on legally-binding assurances that countries which do not use the single currency will not face discrimination as the eurozone integrates further.
But France has made clear that it will resist anything which looks like special treatment for the City of London.
The visit to Paris comes a day before Mr Cameron speaks to leading MEPs in Brussels on Tuesday, and follows his trip to Hamburg on Friday for talks with German Chancellor Angela Merkel - as his round of whirlwind diplomacy gathers pace in the run-up to the two-day European Council summit.