Rangers forward Steven Naismith was left bemused after having a strong appeal for a penalty rejected against Sevilla.
The Scottish side were denied what looked like a certain penalty in the 37th minute when Naismith was felled in the box by Sevilla defender Abdoulay Konko with the score level at 0-0.
Swedish referee Jonas Eriksson ignored claims for a spot-kick and the incident could be seen as the turning point in Rangers' 4-1 defeat.
Konko, who could have been sent off for the offence, added insult to injury for Rangers when he headed Sevilla ahead five minutes into the second half.
Further strikes from Adriano, Luis Fabiano and Frederic Kanoute gave the classy Spanish side all three points, leaving Rangers, who grabbed a late consolation through substitute Nacho Novo, bottom of Group G with one point.
Naismith, who started the game in the lone striker's role, could not believe he did not win a penalty in the incident.
"In my eyes it was a stonewall penalty. The ball ricocheted off their player and I took my touch beyond him and he caught my leg," said Naismith.
"I don't understand why I would go down when I was one on one with the goalie.
"I was disappointed not to get it and obviously it could have been a turning point in the game.
"A few folk have pointed out that he would have been off if the penalty had been given.
"As I said, in my eyes it was a penalty and he might have got a red card.
"You need those things to go for you and last night it didn't."
Rangers midfielder Lee McCulloch was equally frustrated by referee Eriksson's failure to award a penalty.
McCulloch said: "I've not seen it back on television, but what can you say?
"I think the referee said Steven slipped but for me it was a stonewall penalty.
"But you have to keep going and I think we did that."