Levski Sofia bus stoned in Stockholm
AIK fans pelted the visitors' bus with stones and bottles and clashed with police after the goalless draw at the Rasunda Stadium on Thursday. Pictures showed the windows of the bus were smashed.
Levski President Todor Batko was hit by a bottle and said he had never seen anything like it.
"It's shocking," an angry Batkov told reporters. "Sweden is a civilized country and such scenes are completely inadmissible.
"I've been to so many countries and I've never seen such things. I informed the match delegate that we'll most probably file a strong protest to UEFA (European football's governing body)."
The club's media officer and a masseur were hit by stones while two players suffered cuts.
Earlier this month, AIK were fined 15,000 euros by UEFA for crowd violence at their Champions League's qualifying tie at home to Norway's Rosenborg.