The 32-year-old was forced off after 28 minutes of the season opener in a recurrence of the problem that caused his first-half substitution in June’s Champions League final victory against Internazionale.
“It’s serious – a big blow, really tough for us,” Guardiola said. “We have to decide whether he has surgery or no surgery but it will be a few months out. In the next days we will decide on surgery. The injury is a big loss, Kevin has specific qualities. You can lose him for one or two games but for a long time it’s really tough for us. But you have to look forward.
“We have alternatives with different skills, different talents. It’s another opportunity [for others] – life gives you that. I’m pretty sure they will take it.”