The Spanish Football Federation (RFEF) is likely to investigate the racist chanting during Sunday's derby between Atletico Madrid and Real Madrid after the referee mentioned it in his match report.
"I asked the match delegate to make an announcement on the public address system to ask the fans to stop making monkey noises when certain players had the ball," said referee Alfonso Perez Burrull. "As a result... the noises grew louder."
Real Madrid's Brazilian fullback Roberto Carlos was particularly singled out by the crowd for the abuse at certain points during the game at the Calderon which Real won 3-0.
The Spanish Federation only investigates such incidents if the referee notes them in his match report.
Racist abuse at black players has been on the rise in Spain in recent months, but not always mentioned in referees' reports.
Roberto Carlos was also abused during Real's league match against Barcelona but the incidents were not included in the report so no action was taken against the Catalan club.
The last time an incident was investigated the RFEF fined two Albacete fans 6,000 euros ($7,865) each and banned them from stadiums for five months for racial taunts directed at Barcelona's Cameroonian striker Samuel Eto'o during a league match in December.
European soccer's governing body UEFA fined Real Madrid 9,780 euros ($12,820) after racist abuse by some of the club's fans during a Champions League match against Bayer Leverkusen in November.
The RFEF is also investigating the behaviour of Spain coach Luis Aragones following a recommendation by the country's Anti-violence Commission after Aragones made apparently racist remarks about France striker Thierry Henry in October.
He caused further controversy when he defended his comments ahead of November's friendly against England in which he also criticised that country's colonial past.
The match was marred by racist abuse and chanting directed at England's black players by large sections of the crowd.
World governing body FIFA fined RFEF 100,000 Swiss francs ($84,820) in December for the fans' outbursts.
