The Gunners' hopes of ending an eight-year trophy drought are now resting on the UEFA Champions League after Colin Kazim-Richards netted the only goal of their fifth-round tie at Emirates Stadium.
Wenger acknowledged after the match that Arsenal's performance was poor, but has challenged his players to bounce back against Bayern Munich in midweek.
"It is very painful and disappointing to lose a game like that. It is now important to focus on the next game," he said.
"We were not good enough to win today. It's as simple as that.
"Not one defeat is acceptable. You are in this job to win every single game.
"The season is not over. For you maybe, not for me.
"If we feel sorry for ourselves we would be completely wrong. We have a massive game on Tuesday night and we have to show that we some response in the team.
"I couldn't see how we could lose the game because we had a lot of the ball and they had one shot on goal but they defended well and it's the kind of game you can lose if you make a mistake at the back like we did."
Wenger, who controversially left Jack Wilshere, Theo Walcott and Santi Cazorla on the bench, only for Kazim-Richards to score shortly after the trio all came on, said he had no problem with Arsenal fans' jeers at the end of the match.
He said: "What do you expect, people to applaud when you lose a game like that? It's absolutely normal."
Wenger was also upset with the way Arsenal conceded as Kazim-Richards scuffed in a shot on the rebound after Wojciech Szczesny had parried a Martin Olsson shot.
He said: "We made a massive mistake on the goal. I don't want to go into much detail about it."