Luis Suarez admits Barcelona have a "tough year ahead of us" after a 2-0 defeat at Granada.
Ramon Azeez and Alvaro Vadillo netted in either half as Granada moved top of LaLiga, leaving Barca without a win in four away matches this season.
The defending champions, who left Lionel Messi on the bench, are already three points off the pace after losing two of their first five matches.
Striker Suarez said in quotes on AS: "It's a worrying defeat, a defeat that hurts. And a defeat that we have to take a real good look at, because there are lots of things that we have to improve.
"There's a long way to go yet, but these are the types of games that win you the title. We have to be tougher if we're going to win the league. We have a tough year ahead of us."
A win against a side they have beaten 11 times in their last 12 league meetings would have taken Barca top of the table on goal difference.
But despite the introduction of Messi at half-time, it was Granada who took their opportunity to leapfrog Sevilla and Atletico Madrid to the summit.
The hosts went ahead in the second minute through Azeez.
Roberto Soldado robbed Junior Firpo, fed Antonio Puertas and his cross was headed in by the striker from close range, leaving Barca trailing for the fourth time in five league matches.
Granada doubled their advantage in the 66th minute, Vadillo converting from the penalty spot following a handball from Arturo Vidal, who had just come on as a substitute.
"You can't go behind so early," Suarez said. "That made everything that bit tougher for us. We had possession of the ball, but we couldn't make it count. We have to analyse what happened."
Barcelona have lost on the road at Athletic Bilbao and Granada already this season, as well as drawing at Osasuna and Borussia Dortmund, and have scored only two goals.
"What we have to look at is the way we're playing as the away side, because the lack of cutting edge and chances is worrying," Suarez added.
"We're Barcelona, and we have to go out there to win the game – we can't start the way we did."