The Armenia international joined the club as part of an exchange deal that saw Alexis Sanchez move to Manchester United, and picked the Chilean's No.7 shirt to wear domestically.
However, UEFA rules dictate that the same number cannot be worn by two different players in Europe, and he has thus picked the unorthodox No.77 shirt.
Mkhitaryan has been picked to start by Arsene Wenger in their last-32 clash with Ostersunds having settled into life at the Emirates Stadium.
The 29-year-old was less impressive in the subsequent defeat to Tottenham but has kept in place in the side to start in attack alongside Danny Welbeck and Mesut Ozil against the Swedish hosts.
More surprising than Mkhitaryan being named in Arsenal's Europa League squad list was the inclusion of injury-plagued playmaker Santi Cazorla.
Cazorla's injury woes have been well documented, and he told in November of how he nearly lost his foot due to Achilles tendonitis.
Along with Cazorla and Mkhitaryan, Konstantinos Mavropanos has been added to Arsenal's squad, after completing a January move from Greek club PAS Giannina.
Arsenal will be hoping to replicate Manchester United's success in the Europa League in 2016-17, which gave them a spot in this season's Champions League.