If Britain quits the EU it will have to get used to being considered an outsider, he told Le Monde newspaper in comments published Friday.
“Deserters won’t be welcomed with open arms,” he said.
Britons will vote June 23 on whether or not to stay in the EU and the latest polls suggest the outcome is finely balanced.
“If the British were to say ‘no’ (to staying in the EU), which I am not hoping for, life in the (European) community won’t go on as before,” he warned.
“The United Kingdom will have to accept being considered a third party, who we won’t be bending over backwards for.
“If the British quit Europe, then we and they are going to have to accept the consequences from that.
“That is not a threat, but our relations will no longer be as they are today,” he added.
Asked what would happen if Britain voted to stay inside the EU, he said the first thing would be to apply the deal that Brussels had agreed with British Prime Minister David Cameron.
No one had been talking about that during the referendum campaign, he added.
In February, Cameron thrashed out a reform deal with the EU which he said included significant concessions.
But the Brexit debate has divided Britain’s Conservative government with increasingly bitter exchanges between former political allies.