Negotiations for a deal on future EU-UK relations are not due to start until next month, but London and Brussels have already clashed over rules for British financial firms' access to the EU after Brexit.
French Foreign Minister Jean-Yves le Drian said it would be tough to achieve Britain's aim of agreeing a free trade deal by the end of the year, with the two sides so far apart on a range of issues.
"I think that on trade issues and the mechanism for future relations, which we are going to start on, we are going to rip each other apart," Le Drian said at the Munich Security Conference.
"But that is part of negotiations, everyone will defend their own interests."
Clock ticking to end transition period in 2021
Britain formally left the EU two weeks ago but still trades like a member under a transition period ticking down to the end of this year.
The remaining 27 EU states are currently drawing up their terms for the talks on the future relationship, with France in particular pushing for a strong stance, notably on the vexed question of fishing.
France and several other countries want to be able to continue fishing in British waters, while London wants full autonomy and limited access for European fishermen.
The bloc's chief negotiator Michel Barnier has said the EU's top priorities are fishing, security and maintaining fair trading conditions for European companies.
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