Foster will be sidelined for up to 12 weeks after a scan showed he has suffered a stress fracture of a bone in his right foot.
Wales international Boaz Myhill, who returned to training this week after a wrist injury, is likely to step in for Foster.
Manager Steve Clarke said: "I've got two other very good goalkeepers to choose from.
"Boaz did well when he deputised for Ben last season and Luke showed on Saturday he is a more than capable goalkeeper."
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