Police in Bulgaria detained 45 fans of Serbian club Red Star Belgrade after violence broke out on Tuesday ahead of their Champions League qualifying match at Ludogorets Razgrad.
Fans came to blows at a Black Sea resort in Burgas, with two police officers and five civilians suffering injuries.
The fans will go through pre-trial proceedings, police said.
Red Star won the European Cup, the precursor to the Champions League, in 1991.
They advanced to the third qualifying round by beating Maltese champions Valletta last week.