The versatile midfielder has acknowledged that the Catalans now face a tough task to retain their league title.
Barca has dropped to third place in the league table behind Real Madrid and Atletico Madrid following this weekend's results, and the Argentine has all but conceded defeat.
"The league is no longer in our hands," he told club's official website. "I don’t think the defeat in the Champions League affected us, we created a lot of chances, but the ball didn’t want to go in.
"But we can’t make excuses. I think we created chances to score, but football can be like this."
The former Liverpool man then went on to stress that Barcelona must bounce back from Saturday's defeat in Wednesday's Copa del Rey final against Real Madrid.
"We have to pick ourselves up and look forward because on Wednesday we have a final and we cannot fail."