The Italian has hit out at his players after they suffered a last-gasp loss to their rivals on Sunday afternoon courtesy of Robin van Persie's deflected free kick
"I don't know why [this happened],” Mancini told The Sun. “I understood before that the free kick was dangerous. I don't know why it happened."
City fought its way back from 2-0 down to level the scores with minutes remaining but lost out as Robin van Persie struck home a 90th-minute free kick.
The Italian was at a loss as to how his side conceded the late goal, but had harsh words for the porous defensive wall.
"The player shooting was Van Persie and he hit it very well. I called Carlos to return to the wall but I was too far away on the bench," Mancini explained. "I think the wall should have been better. I think in the last second we should pay more attention to this situation.
"If you need to put your face there, you need to put your face there."