Xavi was furious with how Eintracht Frankfurt managed to get 30,000 fans inside the Nou Camp - a notion shared by his players.
It comes after Barcelona were handed a shocking defeat at home in the Europa League and sent crashing out of the competition. The Bundesliga outfit recorded a historic 3-2 win in Catalonia to send them through to the semi-finals.
They got there after going 3-0 up against Barca in 67 minutes, including a screamer from Rafael Borre and a Filip Kostic double. But Xavi's side tried to mount an extremely late comeback when Sergio Busquets bagged a worldie of his own.
Memphis Depay scored a penalty in the 101st minute but it was not enough to draw level and Frankfurt emerged victorious.
And in the Nou Camp were 30,000 German fans to cheer them on, though it remains a mystery how so many were allowed in. There have been issues with Barca's supporters giving up their tickets in the past.
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Xavi said: "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."
Even Barcelona club president Joan Laporta spoke out, admitting: "It’s a disgrace what has happened. I feel embarrassed." And defender Ronald Araujo said: "I was surprised that there were so many people from Eintracht Frankfurt in the Camp Nou stands. The club should look at that."
Before the match, Xavi was keen for Barcelona fans to max out the stadium to give them an extra boost and roar the team onto victory. The atmosphere inside the Nou Camp was electric but this partly down to the mix of supporters.
However, this was still a disappointing result for the Blaugrana, whose 15-match uneaten streak has come to an end in spectacular fashion. The Europa League represented Xavi a real chance to land some early silverware in his Barca tenure.
The former Spain international 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."
Frankfurt will now face West Ham in the Europa League semi-finals after the London side blew Lyon away in France to set up a tantalising tie. The winner will take on either Rangers or RB Leipzig in the final with a British side harbouring real ambitions of lifting the trophy at the end of the season.
