Cadiz have confirmed they are taking the matter of Denis Cheryshev's ineligibility in Wednesday's Copa del Rey tie to the Royal Spanish Football Federation (RFEF).
Real Madrid won the first leg of the last-32 tie 3-1, with Cheryshev opening the scoring, but reports broke during the match that the Russian forward should have been serving a one-match suspension after collecting three bookings while on loan at Villarreal last season.
Cadiz president Manuel Vizcaino suggested in the immediate aftermath of the match at the Estadio Ramon de Carranza that they would ask the RFEF to take action, and that has been confirmed in a statement on Thursday morning.
The statement read: "Cadiz CF have presented in the last few hours before the RFEF, a written complaint of alleged proper alignment of the football player Denis Cheryshev, as agreed unanimously at an extraordinary meeting of the board of directors.
"This morning we have received communication from the RFEF that the letter has been received and they have given a deadline to Real Madrid to present the arguments they deem appropriate.
"The club reiterates its utmost respect for Real Madrid and will not make any further statements until there is an announcement from the Competition Committee, who will dictate the magnitude of what happened."
Cheryshev himself has claimed he did not receive any notification of his ineligibility from the RFEF, telling Madrid's official website: "I did not receive any notification from Villarreal to inform me that I had been banned from playing in the Copa del Rey."
That was backed up by Emilio Butragueno, Madrid's director of international relations, who said: "The club were not notified about the sanction. We did not receive any form of notification from the Federation or from Villarreal and nor was the player informed about the circumstances.
"This is not about looking for someone to take the blame. We are going to wait and see what happens. There is an article 41 of the Spanish Football Federation's Disciplinary Code, that states the possible sanction will not take effect if the interested party is not notified personally and the player was not notified. That is why Cheryshev was playing.
"I spoke to the Federation on Wednesday and we will see what happens. The ruling will be made on Friday and our legal representatives will have something to say. We can say little more, tell the truth about what happened, be cautious and careful. We have talked over the course of the night at the club with everyone involved and there is no record."
Fielding Cheryshev could see Madrid kicked out of the Copa, with Osasuna eliminated from the competition for a similar offence earlier this year.