Adama Traore struck twice in the last 10 minutes to punish City for a sluggish and error-riddled performance.
“It shows that we still have weak points which we have to fix as soon as possible,” German midfielder Gundogan said.
“It’s not that easy to take these things and see your biggest rival win all the time, with things that you can’t control.
“But watching their games and situation doesn’t really help us to be honest—we need to fix our situation and drop as few points as possible.
“We have definitely dropped too many points in the early part of the season. If that’s the case in the next few weeks, the gap will be even bigger, so we have to win as much as possible.”
City now have a fortnight before their next game, a trip to Crystal Palace on October 19.
City have not won at the home of the Reds since 2003 but their victory over Jurgen Klopp’s men at home last season ultimately proved crucial in the final reckoning.
That was Liverpool’s only defeat in a title race they lost by just one point, and came at a critical stage of the season as City cut their lead at the top to four points.
Gundogan said: “We had the same, or a similar situation, last year but at a much later stage.
“That’s a fact we can’t be happy with and we aren’t obviously, but there is nothing else to do but make it better in the next game, which is our target.”