Serbia's Consul in the Turkish capital announced that a 25-year-old Zvezda supporter was stabbed to death in violent scenes prior to Galatasaray's 110-103 double overtime win at Abdi Ikpeci Arena.
RTS reported that trouble broke out when around 400 visiting Zvezda fans were denied entry into the arena, leading to physical confrontation.
"It was an act of hostility and a terrible tragedy... I am distraught," Zoran Markovic, the Consul General, told Serbia's state television RTS.
"We had been warning the Turkish authorities for two days prior to the game that it was going to be a high-risk match and we are now trying to make sure that all Red Star fans leave Turkey safely as soon as possible.
"I also wish to stress that the doctors fought like lions for the young man's life after he was rushed to hospital, the resuscitation attempts lasted five hours but he died because he had lost too much blood."
Galatasaray coach Ergin Ataman, whose team won their third match of the Euroleague season, was quoted as calling Zvezda's fans "terrorists" following the pre-game incident.