Seven-times European champions AC Milan, who won an appeal against a decision to kick them out of the competition for breaking UEFA's break even rule, will meet Olympiakos and Real Betis as well as surprise package FC Dudelange from Luxemburg.
The Gunners have been drawn with Sporting Lisbon, Ukrainian side Vorskla and Azeri champions Qarabag in Group E.
When Mkhitaryan played for Borussia Dortmund in 2015, the German club opted to leave him out of their squad for a Europa League game against Azerbaijani club Gabala.
In relation to the situation surrounding Mkhitaryan, UEFA said in a statement to Press Association Sport: "It is a standard procedure for UEFA to send letters of support to associations, clubs or embassies in order to obtain visas for players in order to be able to travel to another country and play in UEFA competition matches".
PAOK striker Aleksandar Prijovic has continued his fine form from last season, scoring in his opening Greek Superleague appearance of the campaign and netting four times in six Champions League qualifiers. The club spent more than $200 million on players past year under new Chinese owners and failed to comply with UEFA rules monitoring transfer fees and wages.
Scottish champions Celtic are in a group that includes the two Red Bull-owned clubs - Salzburg, a beaten semi-finalist last season, and Leipzig - as well as Rosenborg of Norway.