The Premier League champions, on a unprecedented run of four successive English titles, saw their campaign go from bad to worse with a 2-1 loss at Aston Villa on Saturday -- their ninth defeat in 12 matches in all competitions.
The reverse also marked previously prolific striker Haaland's fifth game without a goal in six matches.
After the game, the Norway international told TNT Sports: "First I'm looking at myself. I haven't been scoring my chances. I have to do better, I haven't been good enough."
City manager Guardiola subsequently defended Haaland, who has scored 108 times for the club since joining in 2022 by saying that "without him we will be even worse" and that "he needs to be delivered the right balls in the right spots".
Guardiola stuck to his theme on Tuesday during a pre-match press conference ahead of Thursday's Boxing Day match at home to Everton.
"It's about us, not just one player," he said.
"When in the past we score goals and Erling was so prolific, helping us, it was because of the team.
"And when you have problems at the back, in the middle, it is for everyone, it is a team, it is not about one player. It would be easy, if it was just one player, the reason why. It's not about that."
The Catalan boss added: "Erling is so important for us, will be so important for us, has been. (We have to) try to do things better, to use him better.
"In this situation, this tendency for all of us (is to say) 'the reason why is this one, and this one and this one'. It's about us, about everyone.
"The guys are running, making effort more than ever. All the tendency 'it's because we don't run, because we don't fight, the reason why is this situation or this player or this manager'... It's not about that.
"It's many little details or big details that make all together not as good as we were. But we have another opportunity on Boxing Day."
