Ammon News - Xavi described Sunday's loss as lowly Almeria as Barcelona's "worst game of the season" as the Catalans failed to capitalise on Real Madrid's derby draw with Atletico to extend their advantage at the top of La Liga.
El Bilal Toure's fine first-half strike earned Almeria their first ever victory over Barca, inflicting only the second defeat of the league campaign on Xavi's men.
Barcelona still top La Liga by seven points over champions Madrid as they chase a first Spanish league title since 2019.
But the setback at Almeria ended Barca's 13-game unbeaten league run and follows a 2-1 defeat at Manchester United on Thursday that ended their Europa League hopes.
Barca face Madrid in a Clasico Copa del Rey semi-final first leg on Thursday at the Bernabeu, with their vulnerabilities starting to show.
"I'm very angry because I think we played our worst game of the season," Xavi told Movistar.
"Above all in the first half, we couldn't move the ball around, we lacked intensity, speed, on a day where we couldn't mess up.
"We did not show the passion [we needed] to win the game. In the second half, yes, but they defended well."
Xavi, already without injured trio Pedri, Ousmane Dembele and Ansu Fati, took a risk and rotated heavily and his team paid the price.
The lowly hosts, starting the game 19th with just one victory in their prior eight league games, were on top and went ahead through Toure's emphatic finish.
The Mali international cushioned a long ball into striker Luis Suarez's path, before spinning and breaking forward at pace.
Suarez lofted a pass over Andreas Christensen and Toure ran on to it, lashing an effort past Marc-Andre ter Stegen and in off the crossbar.
It was only the eighth league goal Barcelona have conceded this season, stopping Ter Stegen adding to his impressive tally of 17 clean sheets.
Ter Stegen said Barcelona would recover ahead of the cup clash against Madrid.
"It's a defeat, it always hurts, it never arrives at a good moment, but we will calm ourselves," said the goalkeeper.
"It's important to charge our batteries for Thursday. We're looking forward and we will achieve what we want to."
Almeria rose to 15th, two points clear of the relegation zone.
"The best team in the league came to us, they're first, and we were capable of blocking them, of taking advantage of the chance we had," Almeria coach Rubi told Movistar.