Haaland had little influence in City's play in the derby, taking only 19 touches and registering only two shots, neither of which hit the target.
His performance at Old Trafford was in stark contrast to when he scored three goals and contributed two assists in the 6-3 drubbing of United in October, taking 35 touches and having six shots.
City coach Pep Guardiola conceded his concern about Haaland's involvement in the aftermath of a defeat which left City eight points adrift of Premier League leaders Arsenal after ceding eight points in their last five matches.
"He had enough touches but it's true that when you are looking at areas and you have to look at him," Guardiola said, adding "we have to find him a little bit more".
The Norwegian striker has scored 21 league goals before the halfway stage of the league campaign, two shy of equalling the 23 goals joint-top scorers Son Heung-min and Mohamed Salah managed over the entirety of last season.
He is well on track to break the league record for 32 goals in a 38-game season, set by Salah in 2017-18. Becoming the first player since Chelsea's Jimmy Greaves in 1960-61 to score 41 goals in one English top-flight campaign is also within his reach.
His immense goal count, however, appears to have come at a cost to City's overall play. After 18 matches they have 39 points, five fewer than at the same stage of last season, while they have conceded double the amount of goals, albeit scoring two more.
Haaland's arrival has also meant the rest of the team have scored fewer goals. City's second top scorer is Phil Foden on seven, with Julian Alvarez and Kevin De Bruyne next, tied on three each.
Last season, when City pipped Liverpool to the title, De Bruyne was the team's top scorer on 15 league goals, while Raheem Sterling got 13 and Riyad Mahrez 11. Eight players scored seven or more goals.
After the derby, former midfielder Dietmar Hamann claimed City were "a better team without Haaland, even if he scores 40 goals this season".
Guardiola, however, insisted his team were still playing how he wanted. "I would say the inconsistency was in terms of results but not performances," he said.
