"UEFA firmly condemns the incidents in Marseille," said a UEFA spokesman. "People engaging in such violent acts have no place in football."
Police fired tear gas at hundreds of English and Russian fans to end a third straight day of fighting in the southern French port.
Marseille's police prefect said an English fan was in a "critical" condition after the clashes.
AFP journalists saw a man with a bloodied face receiving treatment on the ground after suffering a cardiac arrest.