Both players sustained their injuries in Sunday’s 1-1 home draw against Chelsea.
City sit second in the league on 42 points, six behind leaders Arsenal after 20 matches.
"Dias, hamstring for four to six weeks," Guardiola told reporters ahead of Wednesday's home game against 10th-placed Brighton& Hove Albion. "Gvardiol out for a long time.
"(John) Stones, no idea. Not ready for the next games. (Nathan) Ake fine.
"With the spirit that we have, always we can cope. Considering fatigue, we have to see the faces and take a decision tomorrow. Tomorrow we will see."