The winger was involved in an off-the-ball altercation with Ezgjan Alioski, which ended with the Leeds man on the floor.
Referee Anthony Taylor did not see the clash in real time but was summoned to the touchline monitor to review the incident and needed only one replay to make his decision, showing the former Lille man a red card.
Pepe had been handed a start on the right of Arsenal’s front three after his encouraging performances in the Europa League before the international break.
However, he failed to take his chance, flattering to deceive in the first half before his moment of madness ended his afternoon prematurely less than ten minutes into the second half.
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