Arsenal's substitutes' bench was a man short against Bayern Munich on Tuesday after the Premier League side got caught up in red tape.
"He was not qualified to play in the Champions League because I wanted to give him out on loan, so we took him out of the list and UEFA informed us today that he is not qualified," manager Arsene Wenger told reporters.
"Because he was on the bench on Saturday (against Everton in the FA Cup), naturally he was with us but honestly that did not have an impact on tonight's result."
Teams are allowed to pick seven substitutes for Champions League games. Arsenal drew the second leg match 1-1 but lost 3-1 on aggregate.
Image: Ryo Miyaichi
Photograph: Michael Regan/Getty Images
Ozil injury 'serious', will be out for a few weeks: Wenger
CL PHOTOS: How Bayern ousted Arsenal and Costa inspired Atletico
Champions League: Can Arsenal and City create miracles in Europe?
Champions League: Bayern knock out Arsenal; Atletico make quarters after 17 years
Ozil over Champions League penalty miss, says Wenger