De Bruyne is still injured while Haaland's performance seems to have decreased slightly after he recovered from injury and now there is no Kevin De Bruyne to support him so Haaland is having a little difficulty.
Kevin De Bruyne is no longer injured and he returned to play matches for Manchester City several weeks ago, had some impressive matches, scored some goals for them too. He only does not play magnificently like previous seasons but problems probably come from Manchester City system too. This season, they have less options to rotate for finding creativeness and danger in their attacking system. They only have three players for it, De Bruyne, Foden and Silva but last season they had Gundogan and Mahrez.
Depends too much on these players make their attacking system is more easily predictable and opponents can defend their goalkeepers better.
The match against Aston Villa was actually very difficult for Manchester City because they were in the title race, but even though Pep Guardiola rotated players, this did not have a big impact on the performance of the Manchester City team and also what was seen proved that the Manchester City team had prepared for the match against Real Madrid well quite well and they proved to be very focused in the match against Real Madrid compared to matches in their domestic league.
The match against Aston Villa is a big win for Manchester City with a hat-trick from Foden, again Foden saved them in this season. Grealish is back and he can be an ace under sleeves for Pep Guardiola in matches against Real Madrid. Doku is another hope for them but this young player has more bad performances than good ones so far in this season.