That also rules the Belgium international out of Wednesday's Champions League group stage opener with Porto. De Bruyne left the Belgium camp earlier in the week.
"The squad have come back a little better than the previous time (last month)," Guardiola said. "Unfortunately Kevin is out. The rest of the players came back well. 'It's not much but I think Kevin be out for the next games."
City will be able to call upon Sergio Aguero again, however, after the striker returned to full training over the past fortnight.
Aguero, the club's record goalscorer, has not played since the second match of Project Restart in June and suffered a setback from a knee injury over the summer.
"Sergio is training well and we are happy," the City manager said.
"Every team needs their strikers. We've played without them. Sergio is training well and I'm so happy to see him on the pitch after such a long time."