The conduct of Chelsea fans will be investigated by UEFA after incidents that are alleged to have taken place in Hungary.
Chelsea and Arsenal will be pleased with their draws in the Europa League but five-time winners Sevilla face a tough trip to Lazio.
The draw for the round of 32 in the Europa League was made on Monday, throwing up some mouthwatering ties.
AC Milan will have their squad restricted in UEFA competitions and face a European ban if they are not break-even compliant by June 2021.
AC Milan crashed out of the Europa League after losing 3-1 at Olympiacos in their final Group F game on Thursday.
Olympiacos secured progression into the Europa League knockout stages at AC Milan's expense thanks to a 3-1 victory in Athens.