Mkhitaryan made the starting line-up in the Gunners squad that thrashed CSKA Moscow in a 4-1 defeat during the first leg of the Europa League quarter-finals, but was quickly replaced by the manager after picking up an injury.
Arsene Wenger said to the Post-match press conference on Thursday that the Armenia midfielder will be missing the Sunday match against relegation-faced team Southampton.
Wenger said: “He has a knee problem, we don’t know how bad it is, we have to assess it tomorrow morning. He will certainly be out for Sunday.”
The Armenian International had no troubles adapting to life with the Gunners, which has seen him bagged a goal and further creating eight goals in just 12 appearances with the team, since joining up from Manchester United in a Swap deal that saw Alexis Sanchez to Old Trafford.
Mkhitaryan provided an hat-trick of assists in his debut match that ended with 4-1 thrashing of Everton, where Aaron Ramsey scored an hat-trick and Pierre-Emerick Aubameyang bagging is first goal in his debut.
With Mkhitaryan out for an unknown length of time, the former United player will miss the Southampton game and possibly miss out on the return leg of the quarter-finals against Moscow in Russia next week.
Arsene Wenger will be facing a difficult time for a team to select to Russia next week, with Aubameyang claimed to be cup-tied by the UEFA.