Being forced to sell key players like Robin van Persie, Cesc Fabregas and Alex Song has left Wenger with a shell of a side that once used to challenge for the title every season.
Wenger made his comments after losing to United 2-1 in the Premier League clash, marking one of their worst start to a season campaign till now.
"We're very far behind now. At the moment you cannot say that [we are good enough to challenge the top three], because we are far away," the Daily Mirror quoted Wenger, as saying.
"We were poor defensively here. There's no obvious reason for that, apart from the fact we didn't start well and United have quality up front. They score goals against everybody and they are better than us. It's as simple as that," he added.
However, Wenger insisted that the club is still determined to buck up and reclaim its position by the end of the season.
"We've played away at United, City, Liverpool and Stoke, so we've had many difficult away games. But that's what we have to show, and that's what the target is at the end of the season," he said. (ANI )