Tiernan Lynch, Derry City manager, said he had “completely mixed emotions” about the game, which his team lost by a scoreline of two goals to one.
Though proud of his team’s performance, the occasion was tainted “bottles being thrown” and scenes that Lynch feared could “get extremely nasty”.
Lynch’s own son was in the stand, which caused him significant concern as he attempted to keep control on the touchline.
“My own wee man was in the crowd… I know how [others] felt; I didn’t know where he was,” he added.
In a statement, Derry City Football Club said it “unequivocally condemns the violence witnessed at tonight’s match”.
“The club is working closely with UEFA, the PSNI, CSKA Sofia and our security partners to establish the full facts surrounding the incidents,” it added.