Cadiz have filed a formal appeal against Real Madrid for fielding an ineligible player in Wednesday's first leg of their fourth-round tie at Cadiz.
Madrid named winger Denis Cheryshev in their starting XI for the 3-1 win at the Segunda B club, but reports in Spain claim he should have been suspended for the game having been booked three times in the competition on loan at Villarreal last season.
Cadiz said in a statement that the Spanish Football Federation (RFEF) confirmed receipt of their appeal on Thursday and that the RFEF will allow a period of time for Real Madrid to present their defence.
Spanish media report that a decision is likely due on Friday.
"The RFEF has accepted our appeal and time has been given to Real Madrid to present a defense they deem relevant," the Cadiz statement said.
They [RFEF] has also sought different reports which confirm that such an infraction existed.
"Cadiz will again show their respect for Real Madrid and their fans and will not make any type of comment until there is an official statement from the Committee of Competition with an edict about the magnitude of what has happened."
Cheryshev, who rose through Madrid's youth ranks after joining the club in 2002, played on loan for Villarreal last season and picked up a one-match ban after collecting three yellow cards in the Copa.
Having since returned to Madrid, the suspension should have been served on Wednesday. Instead, Cheryshev took the field and went on to score Madrid's opening goal.
RFEF rules specify that if a club field an ineligible player, they face disqualification from the competition -- provided the opposing club lodges an objection.
Osasuna were removed from this season's Copa del Rey in September after fielding Unai Garcia -- who had been sent off against Alaves last season -- in a 2-1 win over Mirandes.
Cheryshev scored the opening goal of the game after three minutes against the third-tier Andalusian side, but news soon spread around the Ramon de Carranza that led to Cadiz fans chanting the Russian winger's name.
He was withdrawn by boss Rafa Benitez early in the second half, being replaced by Mateo Kovacic, after the club were made aware of the error. It is reported that Madrid wrongly thought there was an amnesty at the end of last season which scrubbed Cheryshev's ban.
For his part, Benitez insisted he and the club were unaware of Cheryshev's situation, and weren't informed until after half-time.
"Clearly, the club did not know anything, the federation had not said anything, neither had Villarreal, so we thought we could field him," Benitez said. "As soon as we were aware, after half-time, we substituted him immediately to show good faith."
ESPN FC's Dermot Corrigan and The Associated Press contributed to this report.