French Foreign Minister Laurent Fabius said a British referendum on whether to leave the EU was "very risky", ahead of a visit by Prime Minister David Cameron to Paris on Thursday.
Cameron is carrying out a whistlestop tour of European capitals to push for reforms he says are necessary before the EU referendum, including on immigration.
"We will listen to him and see what he proposes," said Fabius.
"He launched this referendum project, it is something very risky. We hope Britain stays in the European Union, nevertheless there are things that need to be improved."
Fabius said that France was in favour of a simplification of the functioning of the 28-nation bloc.
"But even though we say yes to an improvement of the Union, we cannot agree with its breakup."
After winning this month's election with a narrow surprise majority, Cameron's centre-right government will Thursday publish its first bill which will pave the way for a referendum by 2017 on whether Britain should leave the European Union.
'You can't join a football club and then decide to play rugby'
Cameron said on Wednesday he hoped the measure would pass in "extra quick time" and has not ruled out holding the referendum vote next year.
On THursday his foreign Secretary Philip Hammond said Britain will vote to leave the EU unless European leaders agree to a “substantial package of reform” demanded by Cameron.
"I find this process quite dangerous," said Fabius.
"The British population has gotten used to being told: 'Europe is a bad thing', and the day they are asked to decide, the risk is that they say Europe is a bad thing."
He said that one couldn't "join a football club and decide in the middle of the match we are now going to play rugby."
Fabius said Britain would "certainly" have the most to lose if it left the EU, but that the bloc would also suffer.
Britain "is a military power, a diplomatic power. If such an important country leaves Europe it will give an extremely negative impression of Europe."
Cameron will also visit Berlin and Warsaw on his trip.