BARCELONA • Real Madrid could be thrown out of the King's Cup for fielding an ineligible player in their 3-1 win over Cadiz on Wednesday.
Real's Denis Cheryshev received a third yellow card playing for Villarreal in the semi-finals last season.
He has not served the resulting ban and the Madrid club are set to be thrown out of the competition, Spanish media reported.
Cheryshev scored the opening goal before he was substituted at half-time by Mateo Kovacic.
"Clearly, we didn't know. Villarreal and the federation hadn't warned us," said Madrid manager Rafael Benitez. "When we knew, we substituted him to show good faith."
Isco scored twice after the break before Cristian Marquez's late consolation rounded off the scoring in a 3-1 Madrid win.
But the result could yet prove meaningless if Real are proved to have fallen foul of the competition's rules.
Third-tier side Cadiz's president Manolo Vizcaino has confirmed his club will file a formal complaint.
"We have decided to report the ineligible line-up," he said.
"It hurts us to do so with a friendly club but the decision taken has been firm and unanimous."
Real Madrid director of institutional relations Emilio Butragueno laid the blame at the Spanish Football Federation and Villarreal for not informing the club of the ban.
"It is a complicated situation.
"Nobody at the club knew about the suspension.
"Nobody at the club was informed by the federation, we received nothing from Villarreal and Cheryshev didn't know about the ban," he said.
It is not the first time Madrid have been caught out by an administrative problem this season, after the signing of Manchester United goalkeeper David de Gea fell through as the clubs missed the deadline for the paperwork to be filled.
REUTERS, AGENCE FRANCE PRESSE