Barcelona's last match before the clasico against Real Madrid ended with the Catalans claiming they should have been awarded a late penalty in their 2-2 La Liga draw at Real Sociedad.
The dropped points could cost Barcelona the Spanish league lead as Real face Valencia on Sunday.
Barca will host Los Merengues on Wednesday in a match rescheduled from earlier this season.
On Saturday, Sociedad defender Diego Llorente appeared to pull down Gerard Pique by his jersey in stoppage time, but the referee - and video review - didn't make the call.
The hosts' first goal came on a penalty awarded in a similar situation, as Sergio Busquets grabbed Lllorente's jersey in the box.
"The one on Gerard was clearer than mine," Busquets said.
"If the referee saw the first one, he had to see that one as well. I think he saw it, but didn't want to make the call."
Barcelona were expected to file a formal complaint to the Spanish soccer federation over the no-call incident.
In the evening kick off, Atletico Madrid beat Osasuna 2-0 with second-half goals from Alvaro Morata and Saul Niguez.
A first league victory in their past four games lifted Diego Simeone's side back into the top four.
Elsewhere, Athletic Bilbao were held to a goalless home draw by lowly Eibar in their Basque derby while a late winner from North Macedonia midfielder Enis Bardhi gave Levante a 2-1 win at Granada.
Barcelona coach Ernesto Valverde didn't rest any of his top players against Sociedad, playing Lionel Messi, Luis Suarez and Antoine Griezmann in attack, and dismissed any suggestions his second-half substitutions were with an eye on their upcoming mid-week game.
"We are dying here on the bench and we're going to think about the Clasico? You think about what you have in front of you," Valverde said.
Barcelona, who had won nine of their past 10 league games, were outplayed during most of the match at Reale Arena.
Mikel Oyarzabal opened the scoring for the hosts by converting a 12th-minute penalty before Barca responded with goals from Griezmann on 38 and then Suarez on 49.
Alexander Isak equalised for Sociedad in the 62nd minute.
"We are upset despite a draw against a team like Barcelona," Sociedad coach Imanol Alguacil said.
"We did more than they did, we could have taken the three points."
Australian Associated Press