Partizan Belgrade fans vandalised their team's dressing room and left their head coach Aleksandar Stanojevic, 50, with a head injury after a 4-0 loss to rivals Red Star in Serbia on Monday.
Red Star have won the last three editions of the Belgrade derby and Monday's victory was the biggest since 1998 when they won by the same score.
"Disgruntled fans broke the glass, it's unpleasant. I came with band-aids to the press conference, but there's no reason to make a theatre," Stanojevic told reporters.
"There was nothing more, no fight, no physical conflict. It's no drama."
Stanojevic said the loss was the worst of his career.
"I apologise to every Partizan fan, I apologise for the way we lost the game," he said.
"I take responsibility and this is mine, the worst defeat in my career. It's my fault how we lost the game... it's a shame for all of us. And for me, the biggest."
