The assistant referee has made a formal complaint to anti-corruption authorities, claiming he was pressured into favouring Real Madrid against Barcelona by the league's refereeing committee.
In a court filing published by Spanish radio station COPE on Wednesday, the official, who didn't want to reveal his identity, claims pressure was put on a senior referee who is expected to take charge of the match on November 21st to handle the game in a manner that would "prejudice the interests of one of the clubs involved, Barcelona."
It is alleged the referee in question then contacted the complainant to request he make the more difficult decisions in the match as the referee's performance is subject to more scrutiny by the media.
Moreover, the complainant alleges he also received a phone call from a senior member of the referees' committee advising him it would be "intelligent" to follow the instructions for the progression of his career.
Referees in Spain's top flight are normally allocated to matches little more than week before the games take place.