A UEFA inspector will seek answers from Arsenal and Cologne over the cause of the crowd trouble that marred last week's Europa League meeting.
Chelsea face Arsenal on Sunday, while Man United entertain Everton. All four clubs are balancing European priorities different to that of last season.
Cologne have apologised for the crowd disturbances which overshadowed Thursday night's Europa League match at Arsenal.
Public safety should be paramount, but the hysteria about the breakdown in segregation has its roots in a different era. Football must evolve.
Match was delayed by an hour as thousands of visiting fans outside the stadium prevented Arsenal supporters from getting to the turnstiles.
Would English fans have been given a harder time if they had done what Cologne's did at Arsenal on Thursday night?
Move comes after Arsenal said they would conduct a full review to determine how vast numbers of Cologne supporters gained access to home sections.
Arsenal beat Cologne 3-1 in their first Europa League group game at the Emirates but the headlines were all about what happened beforehand.
Arsenal will conduct a full review to determine how vast numbers of Cologne supporters gained access to the home sections of the Emirates Stadium.
Arsene Wenger thought Arsenal's Europa League game against Cologne would be called off because of the fan trouble outside the Emirates Stadium.
Everton boss Ronald Koeman apologised to the club's fans after the dismal 3-0 Europa League defeat to Atalanta and stressed he was responsible.
A porous defence, a lack of energy, and no attack contributed to yet another loss for Everton.
Man United are still evolving under Jose Mourinho, but thanks to UEFA's technical report on their Europa League win, we can see the signs were there.
Arsene Wenger praised Arsenal's supporters for dealing with a uniquely challenging situation involving away fans from Cologne in the Europa League.
After a delayed kickoff due to crowd issues, Arsenal fell behind early vs. Cologne but rallied with three second-half goals to win big.
Arsenal kicked off their Europa League campaign with a 3-1 Group H victory against Cologne.