Wenger made nine changes to his team but insisted it contained enough quality to beat Forest and reserved criticism for his senior players.
‘We were not good enough anywhere, not up front, in the middle, at the back and we paid for it,’ said Wenger. ‘They looked sharper.
‘I understand the selection will be questioned but we had eight or nine experienced internationals on the pitch, with all respect against a Championship team, and that would be the wrong excuse.
‘Overall I congratulate Nottingham Forest for an outstanding performance. They were winning decisive challenges and were dangerous going forward.’
Wenger defended his selection ahead of Wednesday’s Carabao Cup semi-final first leg against Chelsea.
‘We had a very difficult schedule,’ he said. ‘Many players were on the edge. We play on Wednesday, it was nearly impossible to make it.’
Wenger has won the FA Cup a record seven times, including three in the last four years, but this is the first time he has failed to reach the fourth round in his 21-year stint in charge, and only the second time he has lost to a lower-league club.
“You never put disappointments behind you, but the only thing that can help is to focus on the next game. It’s true that we won the FA Cup three times in the last four years, so it hurts even more because it’s a competition we love,” he said.
“That’s why it’s disappointing that we were not at the level today.”