"Well I expected Djourou to come back from Birmingham [after his loan spell] as a centre back but he was injured," he told arsenal.com. "Also you have to accept that to find a centre back who can play for Arsenal Football Club at the top of the League in January is not easy.
"Of course, I'm not pretentious enough to say I didn't make mistakes. Even if I managed for 150 years I would still make mistakes. In this job, you can never prove afterwards that you were right and nobody can prove you were wrong. Only results prove that. I'm humble enough to accept I make mistakes and I will every year. But I don't know if I made a big mistake this season."