The Greek Super League has hit Panathinaikos with a three-point deduction following fan violence during their 2-1 win over Olympiakos on Sunday.
The match was delayed before kickoff at Leoforos when Pana's Gate 13 ultras entered the pitch to attack Olympiakos manager Vitor Pereira as he walked over to the goal in front of them.
The violence led the Greek government to suspend league matches this weekend.
Panathinaikos were also fined 100,000 euros and forced to play their next two home matches behind closed doors.
The Athens side had closed to within three points of league leaders Olympiakos with Sunday's victory, but that gap is now back to six with nine matches remaining.
"The decision saddens us and is unfair," Panathinaikos said in a statement.
Panathinaikos blamed the trouble on Pereira's prematch comments and the appearance on the pitch of Olympiakos president Evangelos Marinakis, who had been warned not to show himself. Objects were thrown and flares fired at Marinakis, who was uninjured.
The troubles continued in the second half when Olympiakos midfielder Pajtim Kasami was hit by a flare, and police fired tear gas into the crowd.
On Tuesday, league organisers said an executive meeting was broken up after officials from the rival teams were involved in a brawl.
The league suspension was the third this season, after a fan from Ethnikos was killed in Crete in September, and following a November match when a referee was attacked and hospitalised.