The Midlands club saw their perfect record come to an end in their fourth group stage game.
Having won their previous three, Villa lost 1-0 to a penalty when Tyrone Mings picked up the ball inside the area after being passed the ball by keeper Emi Martinez, who was taking a goal kick.
Ex-referee Mark Halsey told The Sun: "We see it week in week out in every league around the globe, where the goalkeeper takes a quick goal kick giving it to the defender, and the defender plays it away."
He then added: "The referee has no option whatsoever to to give that penalty because the ball is in play and it's a schoolboy error by Tyrone Mings.
"It's just unbelievable for a player of his calibre to do what he did in the second half.
"So Aston Villa can have no complaints whatsoever."