Miami coach Phil Neville said DC United forward Taxi Fountas (27) used a racial slur towards Miami defender Damion Lowe (29) during the match on Sunday, calling the language "unacceptable in society".

Fountas has denied the allegations.

MLS said an investigation would "begin promptly".

"MLS has zero tolerance for abusive and offensive language and we take these allegations very seriously," the North American league said in a statement.

Neither team immediately responded to a request for comment.

In an Instagram post, Fountas wrote: "I did not use the word I am being accused of using. We had a hot discussion on the field but I have not racially abused anyone."

Neville and DC United boss Wayne Rooney, former Manchester United and England teammates, talked to the referee Ismail Elfath after the incident.

Neville discussed whether to take his players off the pitch but when the match resumed, Fountas, who had scored to make it 2-2, was immediately substituted by Rooney.

"I must also give massive, massive respect to Wayne Rooney for dealing with it in the way that he did," Neville added.

Inter Miami won the match 3-2 with a stoppage-time goal from former Argentina striker Gonzalo Higuain (34).