Arsenal boss Arsene Wenger was left fuming after his side's 2-1 defeat at Watford on Saturday.
Watford scored their equaliser after Hector Bellerin was penalised for fouling Richarlison but the Frenchman believes Neil Swarbrick decision to assign the penalty was completely wrong.
"The penalty? It was never a penalty. It's unbelievable to lose a game because of that," he told Arsenal.com.
"It's unbelievably hard to take because we had the opportunity to win the game. We played very well in the first half and in the second half we dropped our level a little bit. Physically we were not at the same level and on top of that we missed chances to score the second goal.
"After that we were punished by a bad refereeing decision. There's a lot to swallow tonight and a lot to be really disappointed [about]."
Having pegged us back, Watford grew in stature and created chances of their own before Tom Cleverley rammed in the winner.
"[At 1-1 we should] be calmer and not lift the ball so much, play on the ground and focus more on the quality of our game," said the boss. "I think we became nervous and we lost our composure when it was 1-1."
