PAOK coach Vladan Ivic was taken to hospital after being struck by a beer can thrown by fans during a melee in a match at Panathinaikos.
The Greek rivals were battling in a play-off for a Champions League berth when a brawl erupted following a red card for PAOK's Amr Warda in the 51st minute.
Warda's red card followed an earlier red for Panathinaikos, who went ahead 1-0 early in the match through a Marcus Berg goal.
During the brawl, Ivic was struck in the head by a beer can thrown from the stands and had to be taken to hospital.
The referee was forced to abandon the match in the 55th minute with Panathinaikos still up 1-0.
This is just the latest incident involving fans in Greek football, with PAOK and AEK Athens supporters clashing at the Greek Cup final earlier this month.