Monday's Champions League draw has been overshadowed by controversy after Manchester United appeared to be mistakenly excluded for a brief period.
Former Arsenal player Andriy Arshavin and UEFA head of club competitions Michael Heselschwerdt was tasked with picking the balls, and in a rare mistake saw United drawn against Villarreal, with whom they had already faced in the group stage.
As such, the tie was invalid and Arshavin was told to pick a fresh opponent for Villarreal, which happened to be Manchester City.
UEFA deputy general secretary Giorgio Marchetti apologised for the "technical issue our draw is experiencing", having: "kindly asked for the name of City to be put next to Villarreal."
The ball containing United's name appeared to then be excluded from selection by mistake when Atletico Madrid's opponents were decided.
"For Atletico Madrid, the possibility are all [teams] except for Liverpool, who was in the same group, and Manchester United as they were already drawn."
Atletico were then drawn against Bayern Munich, with the Athletic since reporting the Spanish side are frustrated with errors which led to the tie being confirmed.
United were then put back into play and were eventually drawn against Paris Saint-Germain.
MEN Sport have contacted UEFA for comment.
