Haaland suffered a twisted ankle late in the first half at the Etihad and Guardiola took no risks with City already leading 3-0 at the break.
The European champions host Young Boys of Switzerland in the Champions League on Tuesday.
But with City well on course for the last 16 thanks to three wins from their opening three group games, Guardiola may give Haaland extra time to recover for Sunday's trip to Chelsea in the Premier League.
"Twist in the ankle. We didn't want to take risks with him because he didn't feel comfortable," Guardiola said on Haaland's injury.
"He'll be back maybe Tuesday but maybe next Sunday. Hopefully not a big issue."
Haaland failed to find the net in his 45 minutes on the field, but City were still rampant as they went back to the top of the Premier League.
Jeremy Doku was the star of the show with the opening goal and had a hand in four more.
Bernardo Silva scored twice, while Manuel Akanji, Phil Foden and Nathan Ake were also on target.
