Sterling was not involved for City's shock FA Cup fifth-round defeat at Wigan Athletic last time out, and Guardiola is unsure whether the English forward - boasting 20 goals in all competitions this term - will feature at Wembley Stadium.
"He has a muscular problem," Guardiola said at his pre-match presser when asked for an update on Sterling's fitness. "He had it against Basel. I don't know if he will be ready for Sunday."
Fellow attacker Gabriel Jesus is also expected to miss out, having only managed to get a few training sessions under his belt since damaging his knee against Crystal Palace on New Year's Eve.