Atletico Madrid discovered the issue during their training session on Monday evening and subsequently lodged a complaint with Uefa.
Despite Arsenal resolving the problem approximately 45 minutes before Atletico players were due to return, the Spanish side opted to finish training early and shower at their hotel.
Arsenal manager Mikel Arteta praised Atletico's coach Diego Simeone, highlighting his 'really high level of organisation' and the strong identity he has created at the club.
Arteta also admitted to being inspired by Simeone's passion and his ability to maintain energy and a winning mentality over a long period in a demanding environment.