Leading 2-1 in the second half, City's star striker Erling Haaland ran through on goal and went down after contact with Nottingham Forest goalkeeper Matz Sels.
Referee Darren England did not award a penalty and video assistant referee Tony Harrington felt there was no need to overturn the decision.
It left City captain Bernardo Silva questioning the officials, telling TNT Sports: "We are used to this [happening] this season. All the 50-50s have gone against us.
"The Erling incident – for me it is a penalty. What can Erling do? This season we are used to it. We know how it works.
"Our job is to be better. These things we cannot control. What we can control is our own performances. That is what we must focus on."
Boss Pep Guardiola was not getting drawn into a discussion on the incident, adding: "I spoke weeks ago about that subject.
"I always believe that we have to do it much better so the officials don't intervene. It's our responsibility to do it better, we don't have to rely on them.
"Nothing more to say, I said it in the past."
Former City defender Micah Richards said on BBC Match of the Day: "It was a penalty, don't be so ridiculous. His face said it all. Sels takes him out, it is as simple as that."
But ex-Liverpool midfielder Danny Murphy said: "I don't think, just because there is contact that it is a penalty. It isn't a stonewall one."
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