Midfielder Xavi Hernandez believes Barcelona have to recover the intensity in their play if they are to avoid a first league defeat of the season when they travel to Athletic Bilbao on Sunday.
The Catalans were beaten for the first time in 21 games since Gerardo Martino took charge in July on Tuesday as they produced an insipid display in going down 2-1 to Ajax in Amsterdam in the Champions League.
Defeat was the first sign that Barcelona could be missing the influence of the injured Lionel Messi and Victor Valdes, but Xavi insisted those that are available have to show the right attitude when they face Athletic.
"They are important players and you are going to miss them, but that wasn't the principal reason for the defeat. We didn't do enough to win.
"We need to have intensity from the start and in San Mames it will be another test.
"We need to turn it around and go for it from the kick off with that intensity that we lacked (against Ajax)."
Barca are likely to also be without full-backs Adriano, Jordi Alba and Dani Alves on Sunday, but Sergio Busquets and Alexis Sanchez will return after being rested in midweek.
Bilbao have had an impressive start to their campaign as Monday's 2-1 win over Malaga moved them to within a point of Villarreal in the final Champions League spot.
Ernesto Valverde's side are unbeaten at home since the opening of the new San Mames in September with four wins and two draws from six games at their new stadium.
The visit of the league leaders will prove their biggest test to date, but striker Aritz Aduriz is hoping they can take advantage of Barca's series of injuries.
"They are very important players for them. We will see if we are capable of taking advantage of it, although the other players have all it takes to replace them," he told sports daily Marca.
"To me they seem just as good as always. Until now they have won almost every game. Their level is just as good if not better than in previous seasons."
Real Madrid have the chance to cut their gap to Barcelona to three points for 24 hours at least when they host Real Valladolid on Saturday.
Carlo Ancelotti's men continued their free-scoring form with a 4-1 destruction of Galatasaray in the Champions League on Wednesday despite playing the majority of the match with just 10 men.
Madrid have now scored 26 times in their last six games at home and in Europe and could be boosted by the return of Cristiano Ronaldo.
The Portuguese missed Wednesday's game due to a slight muscle strain, but Ancelotti confirmed that the player himself is confident he will be fit in time to face Valladolid.
And even if La Liga's top scorer doesn't make it, Valladolid boss Juan Ignacio Martinez is aware of the daunting task facing his side.
"It is very difficult to get anything there because they are very good and, moreover, they have gained a lot since the return of Xabi Alonso," he said.
"We will try to compete well and hopefully remove the bad taste in our mouth we had after defeat in the last game against Osasuna."
Second-placed Atletico Madrid are also in action on Saturday away to Elche as they too can put the pressure on Barcelona by moving level on points with the Catalans.
Diego Simeone will recall a number of first team regulars, including Diego Costa and David Villa, having left six players back in Madrid to rest while the remainder of his squad travelled to Russia for a 1-1 draw with Zenit St Petersburg in the Champions League in midweek.
Fixtures (all kick-offs GMT)
Getafe v Levante (1900), Villarreal v Malaga (1930)
Elche v Atletico Madrid (1500), Celta Vigo v Almeria (1700), Real Madrid v Valladolid (1900), Espanyol v Real Sociedad (2100)
Real Betis v Rayo Vallecano (1100), Granada v Sevilla (1600), Valencia v Osasuna (1800), Athletic Bilbao v Barcelona (2000)