The Armenian international arrived at Old Trafford from Borussia Dortmund in 2016. After failing to adjust to life in England initially, the 29-year-old was only able to show glimpses of what he is capable of in a United shirt.
Mkhitaryan started this campaign on a positive note, registering five assists in the first three league fixtures. However, the playmaker failed to make much of an impact on the team in the upcoming fixtures, and he was eventually dropped from Mourinho's starting line-up.
United then allowed the former Bundesliga star to leave the club and make a switch to Arsenal in the January transfer window as a part of the deal which saw Alexis Sanchez move in the opposite direction.
Comparing the playing styles of Arsenal and United, he suggested that the current philosophy at the Emirates suits his game better.
"Everyone knows Arsenal play offensive football, and I love to play offensive football. In Manchester, we were playing offensive football too, but not in every game. So it was quite different," Mkhitaryan told Sky Sports.
"I don't want to blame anyone because every manager at every club has a different philosophy. Maybe, I couldn't fit perfectly in the Manchester United football [philosophy]."
However, Arsenal's footballing philosophies have not helped them much with results in recent times. They suffered a 3-0 defeat at the hands of Manchester City in the Carabao Cup final and will face Pep Guardiola's side in the league again on 1 March.
Arsene Wenger's side are heavy up front, with the likes of Mkhitaryan, fellow January signing Pierre-Emerick Aubameyang, Mesut Ozil and Alexandre Lacazette. There have been suggestions that this has created an imbalance in the team's defence.
However, the ex-Dortmund man does not agree with that view, saying that it is the duty of every player on the pitch to contribute to his side's defence.
"Every player has to defend, it doesn't matter if you are a striker, winger, attacking midfield, you have to defend, you cannot just defend with four or five players, the whole team must defend," the Armenian explained.
"I'm doing my efforts to help the team to defend, sometimes it can work, sometimes it doesn't. But I always try to do my best for the team first of all, and then I'm thinking of myself. I'm not an ego player to think of myself first. Then, when I get the ball, I can create."