Barcelona manager Xavi was perplexed at how more than 20,000 Eintracht Frankfurt supporters were allowed inside the Camp Nou on Thursday for their Europa League clash.
The Catalans lost the game 3-2 and went out 4-3 on aggregate as the Bundesliga side pulled off a huge upset to reach the semi finals of the competition.
The atmosphere inside the stadium was also unusual, as the away fans turned up in uncharacteristically large numbers, leaving the hosts bewildered.
Xavi felt it made the game feel more like a final at a neutral venue, while slamming the "miscalculation" on their part.
He told the press after full-time:
"Clearly the atmosphere did not help and the club is looking into why this happened. The players want to know why too.
"It was a clear miscalculation on our part. This cannot be allowed to happen. It was more like a final with the stadium divided."
Xavi had called for the Barcelona fans before the game to turn up in numbers and ensure a huge atmosphere.
But it turned out, his appeal fell on deaf ears, with only a few thousand showing up, and many of them even left the stadium in the middle of the game.
However, the manager admitted that it cannot be used as an excuse for their shock elimination. Xavi further added:
"The atmosphere is not an excuse. The problem is a football one. We made too many errors.
"We made mistakes in all three goals and we have to look at ourselves. We did not play well. That is why we are out."
Barcelona return to action on Monday against Cadiz in La Liga at the Camp Nou.
Barcelona president "embarrassed" by stadium mishap
Echoing Xavi's words, Barcelona president Joan Laporta was also outraged at how so many Frankfurt fans were allowed inside the stadium.
It was estimated that about 30,000 away fans had come to Barcelona for the match, with many of them having tickets to enter Camp Nou.
However, thousands of season-ticket holders from the home side opted against showing up to celebrate Easter and apparently sold their tickets to Frankfurt fans.
The claim hasn't been confirmed yet but when asked why so many Barcelona fans gave up their seats, Laporta said:
It’s a disgrace what has happened. I feel embarrassed."