Sevilla expressed their “disgust” and asked La Liga to take action after winger Lucas Ocampos appeared to be touched “completely inappropriately” by a fan in their win at Rayo Vallecano.
A fan appeared to poke the winger’s backside while he was preparing to take a throw-in during Monday’s first half.
Ocampos told the referee about the incident before continuing the game.
The Argentina international said he wants La Liga to treat the incident “as seriously as it takes racism”.
“I kept my calm because I have two daughters, I hope this doesn’t happen to them in the future,” he told broadcaster Dazn.
In a statement, Sevilla said: “We would like to place on record our disgust at the incident.
“Lucas Ocampos was subjected to an obscene and completely inappropriate act by a home fan. We hope that the appropriate measures outlined in the regulations will be taken to prevent such behaviour from happening again on a football field, and we have expressed this to La Liga directly.”
Rayo Vallecano said they were working to identify the supporter and would take appropriate disciplinary action.
“This isolated action is solely the individual responsibility of the fan who carried it out,” the club said in a statement.
“Rayo Vallecano is currently working to identify the fan so that, if he is a season-ticket holder of the club, the appropriate disciplinary measures can be taken in accordance with the internal regulations.”
Sevilla won the game 2-1 to move up to 15th in the table, with Morocco striker Youssef En-Nesyri scoring twice.