A Greek supporter of the football club AEK Athens was stabbed to death overnight from Monday to Tuesday, according to local police.
Brawls broke out in the suburbs of the Greek capital between AEK fans and supporters of the Croatian club Dinamo Zagreb.
Violent clashes left at least eight people injured, three Greeks and five Croats.
The first leg of the Champions League is due to take place on Tuesday evening at the AEK stadium in Nea Filadelfia, an Athens suburb.
“Serious incidents took place outside the Nea Filadelfia stadium. A young Greek man was stabbed to death,” Greek police said.
Among the injured is a minor who was hit in the head with a rock, said the public television channel ERT. They are still in hospital.
The 22-year-old stabbing victim was hospitalised before succumbing to his injuries overnight, according to police.
Greek officers made 96 arrests until the early hours of Tuesday morning.
An investigation has been opened and those arrested are to be heard by the prosecutor on Tuesday, according to the Greek news agency Ana.
Around 100 hooligans from the Croatian club were present in the Greek capital, it added.
Deadly football violence has hit Greece before. In February 2022, a 19-year-old fan, Alkis Kampanos, was beaten and stabbed to death in the northeastern city of Thessaloniki, following a match between two rival Greek clubs, PAOK FC and Aris FC.
Last July, seven of the twelve defendants in the case were found guilty of intentional homicide and sentenced to life in prison.