The La Liga giants appear to have fielded a player who should have been suspended for the match.
Real Madrid could be sensationally disqualified from the Copa del Rey for fielding apparently suspended winger Denis Cheryshev.
The Russian, who scored the opening goal of the game, received a suspension after being shown three yellow cards in last season's competition while playing for Villarreal.
As Villarreal lost the semifinal tie to Barcelona in which he received his final booking, that ban has not yet been served.
Cadiz confirmed via its official Twitter account during Wednesday night's match that their board of directors would meet after the game to discuss how to proceed.