Gabriel was sent off for kicking out at Costa, but television replays have shown the Chelsea striker slapping the face of Laurent Koscielny in the build-up to his lengthy altercation with the Arsenal centre-backs.

Asked by BT Sport if he felt a sense of injustice, Wenger replied: "A big one, yes. Because I think Diego Costa should've had a red card, I wouldn't like to be Mike Dean tonight. I cannot understand this situation. Costa, twice should have been sent off.


Diego Costa (right) argues with Arsenal defender Gabriel Paulista. Pics/Getty Images 

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"Look at the situation before the cross comes in. He hits Koscielny in the face on purpose. He makes a fuss of it and in every game he is aggressive and gets away with it because of the weakness of the referee. I think two sendings off for us and Costa staying on the pitch is a shame."

Wenger did admit, however, that Gabriel deserved to be sent off, adding: "Gabriel deserves a red card and I agree, but you expect the referee to make the right decisions. That's all you want."