Sagna was a part of the horrendous defensive display from City at the Etihad Stadium, and he believes that he was not up to the task as he continues to deal with the aftermath of the recent Paris terror attacks.
The Frenchman said: "It was not easy to be part of that event [Paris]. I was feeling down and it was quite difficult to play. Personally, it's not been my best week.
"Mentally and physically I believed I was ok to play. But I wasn't. I tired quite quickly and didn't have as much power as I usually do."
He added: "I felt guilty [about the goal]. I should have kept my head up but I was too upset. I was thinking about what happened and I shouldn't have.
"I don't want to blame the team or the defensive changes we made. I look at myself first and I was bad."