City might have opened the scoring after just 10 seconds, eventually took the lead with two minutes on the clock and doubled it after 20 minutes.
Despite a revival at the start of the second half and Kazuyuki Toda's arrival in the Premiership, the damage was already done.
Glenn reflected: "Disappointment is an understatement because of the way we played out there, particularly in the first half.
"I just couldn't see where that performance was coming from. We've come off a very good performance at Leeds, might have won that game having played Birmingham here and got the three points, there has been a positive stride about us all week, in the dressing room the boys were up for it so to start how we did - they could have scored twice before they opened the scoring.
"I'm scratching my head. Too many players were off for us and it's as simple as that. I don't think we had a player anywhere near his best, everyone was off-key and when that happens you are going to get a poor team performance.
"When you get that you need to fight it more, we needed more desire.
"We were very sloppy from the first minute and that gave them heart. I just cannot believe how we got from where we were in the dressing to the way we started.
"It was a very difficult day and we've let ourselves and the fans down."
Glenn Hoddle admitted he was left 'scratching his head' after our performance in the 2-0 defeat against Manchester City on Friday.