Barcelona are furious with El Clasico referee Juan Martinez Munuera for giving a penalty in Saturday's match - with one Spanish paper discovering that his family are die-hard Real Madrid fans.
The official awarded Real Madrid a controversial 61st minute penalty after Sergio Ramos went down quite easily when Barcelona's Clement Lenglet took hold of the Madrid captain's shirt in the box.
After consulting VAR, Martinez Munuera gave the visitors a penalty at the Camp Nou to the disgust of many Barcelona figures, with Ramos stepping up to score the spot-kick to put Madrid ahead in Saturday's 3-1 victory.
And Spanish news outlet SPORT have discovered that Martinez Munuera's father, Juan Ramon, is a founder of a Real Madrid fan club - Los Amigos de Benidorm - alongside former Valencia president Eduardo Zaplana.
Juan Ramon is also a former referee in the Spanish third division and was known to officiate matches wearing a Real Madrid shirt underneath his referee's uniform.
His other son, Miguel Martinez, was a linesman in Saturday's El Clasico as he lined up for the crucial El Clasico clash alongside his brother.
Barcelona have handed in a complaint to Spanish FA president Luis Rubiales about the officials' performance in Saturday's Clasico.
Juan Martinez has been a referee for 11 years but also works as a policeman in Alicante.
Also in the Spanish press, sports news outlet AS spoke to former professional referee Iturralde Gonzalez, who was unconvinced about Martinez Munuera's controversial second-half call this weekend.
The former official said: 'There is a grab to the shirt, but it is not prolonged, it doesn't last. In my opinion it's a really tight call.'
However, Gonzalez admitted that Martinez Munuera failed to give Real Madrid a penalty earlier in the game that was more clear-cut.
In the 48th minute, Ramos and Lenglet were clashing again at a corner, with the Madrid captain going down following a challenge by the Frenchman.
Gonzalez added: 'Ramos is looking to get an effort off at the front post, VAR does not check it because it would not be deemed a clear and obvious error, but a penalty is not given.'
Mundo Deportivo has also slammed the penalty call during the El Clasico game, choosing the headling: 'VAR Injustice' on Monday morning, claiming that several VAR calls have suspiciously fallen in the favour of Real Madrid in recent weeks.
Barcelona manager Ronald Koeman took a similar tone in his post-match interview, claiming that VAR only acts against Barcelona in the Spanish top-flight.
The Dutch boss told BarcaTV on Saturday : 'Every decision goes against us. 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.'
MARCA, on the other hand, decided to praise Madrid boss Zidane in Monday morning's paper, describing the French boss as the 'winner of the Clasico'.
Saturday's result took Zidane's side to second in LaLiga, one point behind leaders Real Sociedad with a game in hand and six clear of Barcelona - who lie in 12th spot.