The first half of Saturday's match at Elland Road was the subject of an investigation by the Premier League.
After the half-hour mark, the fourth official was called over by the subs and the Premier League confirmed that an allegation of racist abuse was reported by the visitors.
West Yorkshire Police have opened a probe into the incident at Elland Road after making an arrest in connection to the complaint.
A statement from the club said that an investigation was underway and that one arrest had been made in connection to the allegation.
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There are free highlights from the win at Leeds.
Any supporter who is found to be using racist language will be banned from the games for life.
Mikel Arteta told Sky Sports that the stadium manager would have to deal with the authorities over what happened.
It is a single person and we have done a lot in football to try to avoid it. I don't think a full stadium pays the price.
It has to be reported because it was a single incident. The authorities will have to work with the clubs to understand what happened after it was reported.
Gabriel Martinelli scored two goals as the Gunners beat the Whites 4-1.
It was the first away win for the team since October 30 and they got two more goals from Emile Smith Rowe.
It was the only game in the top flight to go ahead on Saturday due to the outbreak of coronaviruses in the league.
The table shows the results of the premier league.
In the race for fourth place, there are four teams with games in hand on the Gunners.
In their last eight matches, Leeds have only one win and are five points away from the bottom of the table.
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