Mallorca fans were filmed racially abusing Real Madrid's Brazilian forward Vinicius Jr. in their Son Moix stadium during their 1-0 upset win against the LaLiga holders on Sunday.
Supporters could be heard calling the 22-year-old Brazilian player a monkey in a video published by streaming company DAZN on social media.
Mallorca did not immediately respond to a request for comment. But in a radio interview club manager Javier Aguirre denied that his players had targeted Vinicius in the ill-tempered match, in which the Brazilian suffered 10 fouls, the most endured by any player in LaLiga this season.
Vinicius has been subjected to racial abuse by fans on at least three occasions - at Camp Nou against Barcelona in November 2021, at Atletico in September 2022 and at Valladolid in late December 2022.
Spanish police are also investigating a possible hate crime against the Brazilian after a mannequin wearing his No 20 shirt was hung from a bridge in front of the club's training centre ahead of the Madrid derby two weeks ago.
The mannequin was hung next to a banner in Atletico Madrid's red and white colours that read "Madrid hates Real" during the early hours of January 26, police said.
Prosecutors in Madrid decided not press charges over racist chanting aimed at Vinicius in September after finding it had "lasted a few seconds" and had not constituted a crime.
In December, Vinicius accused LaLiga of continuing to do nothing about racist fans at matches, after videos on social media showed some shouting abuse and throwing objects at him during a match the previous day at Valladolid.
Pele, Neymar and other leading Brazilian figures leapt to the defence of Vinicius in September after a panelist on a Spanish soccer show criticised the forward.
The panelist said Vinicius was not respecting opponents with his celebrations, comparing his behaviour to that of a monkey - which immediately sparked a backlash on social media.
Vinicius issued a two-minute video statement at the time in response to what he called a "xenophobic and racist" insult, saying he "won't stop dancing" and that "the happiness of a black Brazilian being successful in Europe bothers" many people.
Real Madrid coach Carlo Ancelotti and Vinicius's teammates have been urging LaLiga and authorities to take action to protect the Brazilian from what they are calling "a hunt" by rivals' defenders.
Having suffered 79 fouls so far this season, Vinicius is the most fouled player in Europe's top seven leagues by a big margin, followed by his countryman Neymar at PSG with 59 fouls.