UEFA opened an investigation into Bayern Munich's Leon Goretzka this week, after the midfielder was pictured wearing a Bundesliga shirt during his side's 3-1 Champions League defeat to Liverpool last Wednesday.
The German side have been charged by European football's governing body for the mistake, which broke UEFA's rules on sponsorship on shirts during European matches.
The reason it broke those rules is because, unlike their Champions League shirt, Bayern's Bundesliga shirt features both their T-Mobile sponsor on the front and the Qatar Airways logo on the left sleeve.
Generally, UEFA Champions League shirts have the competition logo on one side, and the logo for their 'Respect campaign' on the other sleeve where a sponsor logo would be during domestic games.
Article 28 of the UEFA kit regulations allows for only one sponsor during Champions League games. The sponsor must be positioned on the front of the shirt without exceeding the 200cm x 200cm measurement limits.