MLS has opened an investigation into allegations that Philadelphia Union defender Kai Wagner directed a racial slur at New England Revolution forward Bobby Wood during last Saturday's MLS Cup playoff match between the two sides, sources confirmed to ESPN.

Sources confirmed to ESPN that Wagner is alleged to have called Wood a racist term in German used against Asians. Wood's ancestry is part Japanese and African-American. Wagner is a native of Germany, and Wood speaks German, having played in Germany at youth and professional level for 14 years.

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The sources spoke on condition of anonymity because they weren't authorized to publicly discuss the allegation. One source added that the league hopes to conclude interviews with the parties involved later this week, at which point MLS will render a decision.

The second match of the three-game series between the two teams is scheduled for Nov. 8.

The Athletic was the first to report the news.

A Revolution spokesperson declined to comment. The Union didn't respond to a request for comment.

MLS issued the following statement: "MLS is aware of the allegation that a player used discriminatory language toward an opposing player, and a review of the matter is underway. The League has been working with the MLS Players Association and Black Players for Change on a process to address these types of allegations and will have no further comment during the pendency of the review."

The alleged incident took place around the 86th minute, following a foul committed by New England forward Giacomo Vrioni on Philadelphia defender Nathan Harriel for which he was cautioned.

This sparked a series of confrontations between Revolution and Union players that involved pushing and shoving. In the video from the match, Wood and Wagner can be seen arguing.

One source with knowledge of the incident told ESPN that Wood told some teammates on the field what happened.

Those teammates relayed the incident to the New England bench, who then informed the fourth official.

That official later told referee Pierre-Luc Lauziere, and he made note of the complaint in his official match report, which triggered the investigation by the league.

Wagner, 26, is widely expected to leave the Union at the end of this season, given that he is in the final year of his contract with the club.

In his five seasons with the Union, Wagner has been named an MLS All-Star in 2021 and 2022 and was an MLS Best XI selection in 2022.