A petrol bomb was thrown and police clashed with Ajax supporters during the Dutch club’s 2-0 Champions League win against AEK Athens in Greece.
Home supporters reportedly threw flares into the stands housing Ajax fans and pictures show flames burning next to the away section.
Images also show police officers hitting Ajax fans, leaving some with blood pouring down their faces.
Ajax defender Matthijs de Ligt ran over to the visiting fans to plead for calm.
At the start of the second half there were further crowd disturbance as several firecrackers were set off.
Players from both sides were seen to be rubbing their eyes as smoke drifted across the Athens Olympic Stadium.
Ajax secured victory through two goals from former Southampton forward Dusan Tadic to progress to the last 16 for the first time since 2005.
AEK, who had Marko Livaja sent off for two yellow cards, are bottom of Group E without any points.