The Spanish and European champions gave up a two-goal advantage to draw 2-2 at Real Sociedad in La Liga last weekend, before conceding a stoppage-time equaliser at home to AC Milan in a 2-2 draw in Tuesday's Champions League Group D game.
Spain playmaker Xavi admitted the team had taken their foot off the gas in the second half at Sociedad, but insisted that Milan's last-gasp goal had been "totally unfair".
"It's pretty clear that we could have done without the first and last thirty seconds of the game," the 31-year-old told Barca's TV channel, after Alexandre Pato had given Milan the lead 24 seconds into the match and Thiago Silva netted a 92nd-minute equaliser.
"But sometimes football is unjust like that, and this time we were on the receiving end," he added. "The team is a bit down, we can't explain it but we have to carry on.
"We're playing good football, but we have to play with more intensity at certain times."
Barca's night was further soured on Tuesday when midfielder Andres Iniesta was forced off shortly before half-time with a hamstring tear that will sideline him for around a month.
The Spain international, who has been plagued with leg muscle injuries in recent years and almost missed last year's World Cup, joins Chilean forward, new signing Alexis Sanchez and central defender Gerard Pique on the injury list.
Barca's great rivals Real Madrid are bidding to end the Catalan club's three-year grip on the Spanish title and top the standings after two matches, a 6-0 demolition of Real Zaragoza and a 4-2 win over city neighbours Getafe.
Jose Mourinho's side play at Levante on Sunday with a question mark hanging over the availability of Portuguese forward Cristiano Ronaldo.
Ronaldo needed several stitches in his right ankle after Wednesday's 1-0 Champions League win at Dinamo Zagreb and complained after the match he and other top players did not get enough protection from referees.
"It's worrying to see Cristiano Ronaldo receiving stitches in the dressing room," assitant coach Aitor Karanka, standing in for the banned Mourinho, said at a news conference. "All players should be equally protected."
Early surprise package Real Betis, who have won their first two games following promotion from the second division are third on goal difference behind Real and Valencia, play at Athletic Bilbao.
Bilbao's Argentine coach Marcelo Bielsa is still without a win in his first campaign in charge at the Basque club following stints at the helm of his native country and South American neighbours Chile.
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