Real Madrid head coach Jose Mourinho says the Negreira case could become “the biggest scandal in world refereeing” if no action is taken.
Barcelona are under investigation over payments made to Enriquez Negreira, a former vice-president of the Technical Committee of Referees.
“If nothing is done, this will become the biggest scandal in world refereeing,” Mourinho said.
Barcelona president Joan Laporta has previously insisted the club committed no wrongdoing and accused Real Madrid of exaggerating the case.
Barcelona have said the payments to Negreira were not made for refereeing decisions, but for reports and analysis concerning refereeing.