Major League Soccer launched an investigation on Sunday following allegations that Portland Timbers player Diego Chara was racially abused during a match against Minnesota United.
Timbers manager Giovanni Savarese said Chara had been abused by an opponent during his team's 1-0 loss to Minnesota on Saturday, and accused match officials of failing to take the incident seriously.
"I am very and extremely disappointed that still at this time we have to deal with situations that should not be happening anymore or in any sport or anywhere," Savarese said.
"It's things that are not acceptable and in this game there was a situation that had to do with a racist situation. A discriminatory word that has been said to one of our players that cannot have any place in anywhere or in any situation or any sport, nowhere.
"So, I'm extremely disappointed that still at this time we have to deal with these kind of situations in a game. The referee should have handled this situation in a much better way.
"I am extremely disappointed that it was not taken as seriously as it should have been."
In a statement on Sunday, Major League Soccer said it was investigating the incident.
"MLS has zero tolerance for abusive and offensive language, and we take these allegations very seriously," the league said.
"An investigation into this matter has already begun. Further information will be provided upon the completion of that investigation."
In a statement issued later Sunday, Minnesota United said the player allegedly involved in the incident denied abusing Chara.
"The team has been investigating the matter and the player involved in the reported incident has denied making any derogatory remarks," the club said.
"We will support the league in any investigation it chooses to make around the alleged event.
"MNUFC is built on inclusivity and respect and does not tolerate discrimination under any circumstance."