The 25-year-old limped out of his side's 2-0 defeat at Tottenham Hotspur on Sunday and could miss a crucial part of the season as City chase silverware in Europe, the FA Cup, and the League Cup.
"It takes weeks, but I don't know how long right now," Guardiola said, as reported by BBC Sport.
City's upcoming cup matches:
|Feb. 26||Real Madrid||Champions League round of 16|
|March 1||Aston Villa||League Cup final|
|March 4||Sheffield Wednesday||FA Cup fifth round|
|March 17||Real Madrid||Champions League round of 16|
Sterling has featured in 23 of City's 25 league outings this season but his form has suffered in recent weeks. Following an explosive start to the season, the English international has failed to score in his last seven appearances across all competitions.
Frontline help may soon arrive in the shape of Leroy Sane, though. The German winger was sidelined in early August with a serious knee injury but returned to training with the first-team squad this week. "It needs time. He needs weeks," Guardiola warned.