A Wayne Rooney hat-trick, a brace from Ashley Young and strikes from Danny Welbeck, Nani and Park Ji-Sung consigned Wengerâ€™s men to their heaviest league defeat under the Frenchman.
Theo Walcott had pulled a goal back for the Gunners before the break and Robin van Persie lashed home with 15 minutes left, but the Arsenal manager could only watch on in horror as his team capitulated at Old Trafford.
â€œIt is terribly painful,â€ said Wenger, whose side were reduced to 10-men for the third successive league game when defender Carl Jenkinson was shown a second yellow card with the score at 6-2.
â€œOf course it hurts, itâ€™s humiliating, but you could see that we had not recovered physically in the second half from Wednesday night.
â€œWe were short in some areas, that is for sure. They have class and they punished us. It was 3-1 at half-time and I think that was harsh against us.
â€œWe tried desperately to get back but we opened ourselves up and were punished. Their finishing was great today.â€
Wenger moved to try and reassure Arsenal fans that will look to re-enforce his squad before the transfer window closes on Wednesday night.
A deal for Monaco striker Park Chu-Young appears to be close, but the Frenchman says the Gunners still need to bolster their defence and midfield.
â€œI am very open if we can find the right players,â€ he said. â€œWe have the money to sign players. If we find players who can strengthen our team then we will do it.
â€œBut I am not the only one to work on the case, we have 20 people who are working on that. If we do not do it, it is because we donâ€™t find them.
â€œWe are close to signing a striker at the moment but we are still looking for a midfielder and a defender.â€
Meanwhile, Manchester United manager Sir Alex Ferguson admitted his surprise at the final score, adding that criticism of his Arsenal counterpart is â€œunfairâ€.
â€œIt is a surprise because when you play Arsenal you expect a difficult game,â€ said Ferguson. â€œIf you look at Arsenal the team is weakened â€“ but we still did the job.
â€œWe got careless at times and they made chances because they still have quality up front But overall we are very satisfied that we kept the performance levels up.â€
He added: â€œI think it is unfair to criticise him [Wenger]. The job heâ€™s done for Arsenal and the philosophy he has â€“ he has given Arsenal some very entertaining players.
â€œHeâ€™s also sold well and looked after the Arsenal coffers. People forget these things. Itâ€™s a cynical world now and when you lose a few games the judges come out.â€
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