The Russian was named in Rafa Benitez’s starting line-up for the last-32 clash in the Andalusian city, and scored the opening goal of the match inside five minutes as Real went on to win 3-1.
But the Russian should not even have been on the pitch: he was on loan at Villarreal last season, and picked up three yellow cards, earning himself a one-match suspension.
Real took him off at halftime when they apparently realised their error but Cadiz filed an official complaint.
There has been no official word yet but Sky Sports’ Spanish correspondent Guillem Balague took to Twitter to break the news that the club had been expelled from the competition.
Spanish radio station Cadena Ser also reported the news, and said the Spanish football federation (RFEF) had told Cadiz of the decision to expel Real.
Madrid are expected to appeal the decision to RFEF’s appeal committee. Should that appeal be thrown out, then the capital club are expected to take their claim to the Court of Arbitration for Sport.
The RFEF is expected to announce its decision later on Friday.
Real president Florentino Perez said on Thursday he believed the club had not broken the rules as neither Cheryshev nor the club were notified he was banned.
It is the latest embarrassment for the world’s richest club by income, whose attempt to sign Spain goalkeeper David De Gea from Manchester United on the final day of the transfer window in August ended in farce when the paperwork did not arrive on time to complete the deal.