The Hall of Famer added that he hopes to have the freshman star back after Christmas and that Stanley will undergo an MRI on Saturday to confirm the injury.
"Cassius' injury isn't a knee injury, we think it's a hamstring but we'll know more tomorrow," Krzyzewski said. "We're thankful it's not a knee injury but we don't know how much time he will miss."
Stanley hurt himself attempting a transition layup early in the second half. He tried to retreat back on defense but pulled up at midcourt.
The 6-foot-5 guard was clutching his leg and needed to be helped off the court by teammates.
Stanley entered Friday's contest second among Duke players in minutes (28.4) and third in scoring (14.1). He posted four points and three assists prior to exiting.
Duke eventually defeated Winthrop 83-70 to improve to 7-1 on the season.