Arsenal did enough to advance, but Thursday's loss to Östersunds FK showed that Arsene Wenger's fringe players aren't ready for the big matches.
AC Milan sporting director Massimiliano Mirabelli said that he felt "sorry for Arsenal" after they were drawn together in the Europa League.
Arsenal will face AC Milan in the Europa League round of 16, while Borussia Dortmund will take on FC Salzburg.
Bilbao mayor Juan Mari Aburto has threatened to withdraw as a host city for Euro 2020 if UEFA fails to take action against football violence.
AC Milan boss Gennaro Gattuso highlighted his side's defensive performance in their 1-0 win over Ludogorets in the Europa League on Thursday.
Peter Stoger said there were "a lot of issues" to be addressed after Borussia Dortmund's fortunate 1-1 draw away to Atalanta in the Europa League.
Napoli boss Maurizio Sarri has admitted regret in his side's elimination from the Europa League on Thursday.
Brendan Rodgers claimed Celtic needed more courage against Zenit St Petersburg after the Hoops crashed out of the Europa League in Russia.
Dortmund striker Michy Batshuayi has claimed he was the subject of alleged racist chants from Atalanta fans during Thursday's Europa League game.
Milan cruised to a 4-0 aggregate win over Ludogorets, as Alessio Romagnoli played a central role in the Italian club's fourth consecutive clean sheet.
Borussia Dortmund were more lucky than good in beating Atalanta, with Mario Gotze a 6/10, but it's simply not good enough.