Just five minutes into the second half, Pepe was spotted on cameras bringing his head towards Ezgjan Alioski and referee Anthony Taylor brandished a straight red to after watching replays on a pitchside monitor.
Arsenal, who lost 3-0 to Aston Villa before the international break, were second best for the majority and will be relieved to come away with a point.
Asked by Sky Sports about Pepe's red card, Arteta bluntly replied: "It is unacceptable. Unacceptable. At this leve you cannot do it.
"Considering how early we got Pepe sent off we have to take it. I never like a draw but in the circumstances it's a point. It is unacceptable."
He added: "With 10 men it is a big disadvantage. I really liked the personality of the team when Pepe let the team down, how we stuck to do what we had to do and had a moment or two to win the game, but obviously it makes it really difficult."
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