José Manuel Barroso has warned that efforts to create a two-tiered EU could spell disaster for the wider European economy.
The EC president was responding to reported plans in France to redraw European economic power in light of the sovereign debt crisis gripping the eurozone.
In a speech in Berlin, Mr Barroso said a new union of stronger economies within the EU could lead to a 50 per cent cut in European GDP.
"Populism and sometimes even nationalism raises its head across our continent," he said.
"This is ignoring the global realities as well as our common history that teaches us that this continent is simply too small and too inter-dependent for us to stand apart, to turn our backs to each other."