Man City had great last season as they finished 3rd on points table and they started last season by winning all 3 of their initial games. But this season they are having disastrous start as they have lost 2 of three games they have played. The start of tournament is important as it tells the moral and strength of team, if team start losing points in beginning of tournament then it's difficult for the team to make a come back at later stage of the tournament. Man City need to win matches if they want to remain in the contest.
If you predict football like this will not get it right, this is just three games, out of 38 games. You don't expect Manchester city to win the whole 38 games. It's better you have a slow start of the season than to have a slow end when it matters most. Other team will still lose more than them. But I truly understand your point, it will reduce the confidence of the player, when you lose like this, but the good news that the players are all playing in their various nations at the intentional break. They will come back with more energy and confidence to face Manchester United. It will be a difficult game for both team, because they are both struggling in the league.
Manchester city, struggle at end of last season, yet they were able to finish 3rd, they start to struggle last season because of the coach pep Guardiola divorce, it affected the team performance , because the coach wasn't mentality strong. The club has to give Pep Guardiola some break, to fix himself. Manchester city game plan is not improving at tall, and if nothing is done about it, they will end badly this season. Pep Guardiola has done his as best for the Club, but right now they need a new coach to put the team together.