Police in Bulgaria detained 45 fans of Serbian club Red Star Belgrade after violence broke out on Tuesday ahead of their Champions League match.
Brendan Rodgers has played down his central defensive problems ahead of Celtic's Champions League third-round qualifier against Astana on Wednesday.
Turkey's Sports Minister has said extra security measures will be in place for Fenerbahce's Champions League qualifier at home to Monaco on Wednesday.
Roma will be watching their prospective Champions League playoff opponents with interest, as reaching the tournament is crucial to their season.
PSG goalkeeper Kevin Trapp says their goal for this season is to be more competitive in the Champions League.