Athletic Bilbao forward Inaki Williams has said he was racially abused during Saturday's 1-1 draw away to Espanyol.
Williams, 25, who signed a nine-year deal baover with Athletic in August 2019, said: "No black player or any player ever wants to hear that."
In a separate incident on Saturday, there were violent clashes outside the Mestalla Stadium before Valencia's win over Barcelona.
La Liga president Javier Tebas said both incidents were a "step back."
Espanyol said they were investigating "incidents of a racist nature uttered by a few against Inaki Williams".
In a statement, the Barcelona-based club said: "Espanyol strongly and explicitly condemns any sign of racism on soccer fields."
It has been reported that Williams told Athletic เกมยิงปลา captain Iker Muniain about the abuse, who then informed referee Jose Sanchez Martinez.
"No black player or any player ever wants to hear that," Williams told the Athletic Bilbao website after the game.
"It's completely out of order, people should go to matches to enjoy themselves, to support their team; football is a team sport and should be played in a friendly atmosphere.