Guardiola taking no risks with Haaland due to minor muscle injury
City were beaten 4-1 on penalties by Barcelona after drawing 2-2 in Florida. Haaland was also replaced at half-time in their 3-2 loss to AC Milan in New York at the weekend.
"He's got some niggles. He didn't feel good," Guardiola said late on Tuesday. "(It is) disturbing something, he doesn't feel comfortable.
"Muscular niggles is not worth the risk. Sooner or later he has to take a step. To lose him for three weeks, that would be a problem as 60-70% of the squad are on holiday."
Premier League champions City play FA Cup winners Manchester United in the Community Shield on August 10 before beginning their league title defence with a trip to Stamford Bridge to face Chelsea on August 18.