Barcelona suffered defeat against bitter rivals Real Madrid in El Clasico on the weekend.
Both sides went into the game far from their best.
And it was the away side that took the lead after just five minutes through Fede Valverde.
Barca weren't behind for long, though, as Ansu Fati netted the equaliser three minutes later.
But Sergio Ramos restored Los Blancos' lead from the penalty spot in the second half, before Luka Modric struck to clinch victory for Zinedine Zidane's side.
Barca would have felt hard done by in the game.
Real Madrid were given a penalty in the second half that could have gone either way. Ramos appeared to go down easily under contact by Clement Lenglet.
And now Barca have submitted a complaint to the Spanish FA after details emerged about the referee, Martinez Munuera's.
It is claimed by Sport that Munuera, a referee of 11 years, has close ties to Real Madrid.
They have discovered that Munuera's father, Juan Ramon, is a founder of a Real Madrid fan club - Los Amigos de Benidorm.
Ramon is also a former referee in the Spanish third division and officiated matches wearing a Real Madrid shirt underneath his referee's uniform.
Barcelona are said to be furious and want action to be taken.
This is obviously a big revelation if true. It's unknown whether Munuera himself is a Real Madrid fan.
But given his family are die-hard fans of the club, he shouldn't be officiating any Madrid games. To be honest, he probably shouldn't be refereeing any Barcelona games either.
Barca manager Ronald Koeman had words with Munuera after the game and complained to the media about the officiating team in his post-match press conference.
"Every decision goes against us," he told Barca TV, per the Daily Mail. "In five games there have been none in our favour. I don't think it's a penalty. VAR in Spain only acts against Barcelona."
It will be interesting to see how this story develops in the coming days and whether the Spanish FA decide to act.