Violent clashes between groups of ultras led to nearly 100 arrests.
ADVERTISEMENTA 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.
Trouble came ahead of the first leg of the Champions League, due to take place on Tuesday evening at the AEK stadium in Nea Filadelfia, an Athens suburb.
Large groups of supporters attacked one another near the stadium, throwing stun grenades, stones, incendiary devices and other objects. Some had bats.
"Serious incidents took place outside the Nea Filadelfia stadium. A young Greek man was stabbed to death," Greek police said.
The 22-year-old victim was hospitalised before succumbing to his injuries overnight, they added.
Among the injured was also a minor who was hit in the head with a rock, said the public television channel ERT. They were still in hospital, as of Tuesday afternoon.
Greek officers made 96 arrests throughout the night until the early hours of the morning.
The violence began about an hour and a half after the visiting side from Croatia left the pitch under police escort.
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.
Greece's main left-wing opposition party strongly criticised the lack of police control over their presence in the city.
"Croatia hooligans - with a long history of far-right ties and violent attacks - crossed the country with one goal: to cause trouble... Were they being watched by the Greek authorities? Were there any preventive checks on their route?", asked Syriza in a press release.
Management at the Croatian club Dinamo Zagreb said in a statement on Tuesday they "strongly" condemned the clashes.
They noted UEFA had made the decision that the two matches will be played without visiting club supporters and urged more Dinamo fans not to travel to Greece.
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.
It was the third death in three years due to fan violence in Thessaloniki alone.
ADVERTISEMENTLast July, seven of the twelve defendants in the case were found guilty of intentional homicide and sentenced to life in prison.
The government raised the maximum jail term for violent fans from six months to five years after Kampanos's killing.