The Gunners have slipped off the pace in the league and were sent crashing out of the Champions League by Liverpool on Wednesday.
The French centre back claims Arsenal have overachieved in making strong challenges in Europe and on the domestic scene, but admits that having led the way for such a long spell their poor run feels like a failure.
"The morale is very low," he told The Times. "Now it will be hard to bounce back.
"Nobody expected much from us at the start of the season and we have overachieved, but when you get this far, it still hurts."