The England international will definitely miss Wednesday's game against West Ham and is a doubt for the Champions League tie with Real Madrid next week.
Guardiola said ahead of the initial date for their meeting with West Ham it will take "weeks" for Sterling to recover – but admitted he could be without him for months.
“It’s a hamstring and we will see,” he said. “It takes weeks, but we’ll see if he is ready for Leicester, Madrid and the rest of the games. I don’t know (if it will be weeks or months).
“It’s a problem, but it’s a problem we had with (Ilkay) Gundogan, (Aymeric) Laporte this season for four or five months. It is what it is. It’s a problem with this kind of season, particularly for the players.”
Better news for City is Leroy Sane’s recovery from knee ligament damage.
The Germany winger is back in full training after missing the first five months of the season.
Guardiola added: “He’s started to train. He’s still not there, he needs to recover, tempo, rhythm, confidence, don’t think about the injury. He needs time, he’ll be there. It’s not like ankle or muscular.
“It’ still needs time. He needs weeks. What’s important is he’s recovered well, he’ll come back stronger than before, but now he needs time.”
Manchester City predicted XI (4-3-3): Ederson; Walker, Fernandinho, Laporte, Mendy; De Bruyne, Rodri, Silva; Mahrez, Aguero, Bernardo