Some sloppy defending, most notably by the Gunners' German centre-back Per Mertesacker, contributed to Arsenal's surprise 3-2 defeat at Swansea on Sunday and Wenger refused to protect his back four.
Successive league defeats have left Arsenal four points behind fourth placed Chelsea and 10 behind third placed Tottenham, putting them in real danger of failing to qualify for the Champions League.
Wenger acknowledged the defence needs to improve quickly and said: "I felt that there were some odd turning points, like when we went to 2-2 we straightaway made a defensive mistake.
"It was similar for me to the Fulham match, a lack of appreciation of the ball. Our defensive performance was not good enough and that is why we lost the game.
"When we came back to 2-2 I thought we had a good chance to win the game because we looked dangerous.
"Their keeper kept them in the game and made some great saves and we missed some unbelievable chances that are difficult to understand and explain.
"Apart from all of that, well done to Swansea. They played well and deserved to win."
Wenger also criticised referee Michael Oliver for awarding a penalty to Swansea which he described as "complete imagination".
Robin van Persie had given the Gunners a fifth-minute lead only for Oliver to point to the spot just 11 minutes later when Nathan Dyer went to ground under pressure from Aaron Ramsey, which Wenger branded a "good dive".
Scott Sinclair scored the resulting penalty and Dyer also got on the scoresheet before Danny Graham scored a 70th-minute winner within seconds of Theo Walcott having levelled matters.
"The game was difficult because Swansea played well and also it was decided by some strange decisions," Wenger said.
"The first one is by the referee who gave a penalty that was complete imagination and a good dive. Well done to the player who did it."
Wenger was impressed by Thierry Henry's latest cameo even if the French striker could not inspire them to victory this time around.
Henry, who scored the winner against Leeds in the FA Cup after coming off the bench last week, is back at Arsenal on loan from New York Red Bulls, but he couldn't grab a goal in his first Premier League appearance for five years.
"You are always tempted. I know he wants to help the team out. When he comes on the pitch he gives us a lift. He was dangerous again when he came on," Wenger said.
Swansea manager Brendan Rodgers hailed his players for their heroics in achieving what he felt was their biggest scalp since their promotion to the Premier League.
"You come up against a top club with a world class manager and to come out with a victory and performance like that is an incredible day," he said.
"I am very proud of the players and it?s a wonderful day for the city. It is the biggest scalp we have had so far."
And Rodgers felt Graham, Sinclair and Dyer did their England prospects no harm in front of the watching Fabio Capello.
"I am sure he (Capello) would have been surprised at the level the players played their game," Rodgers said.
"They were a massive threat and it has probably given him something to think about, I'm sure.
"I think the advantage my players have is that they play a style of football that if they went to international football it would be no surprise for them."