The league defeat was Barcelona's second in the space a few days after they exited the Champions League quarter-finals to La Liga title rivals Atletico Madrid last Wednesday.
"Mentally we're pretty screwed up," he told the club's official website.
"We could have won but we couldn't capitalise on our chances. We gave it our all but in the end it wasn't possible. We will fight for the league until the end, we still have games left and hopefully our rivals lose points."
Barcelona face Real Madrid in the final of the Copa del Rey on Wednesday.