Randolph went up for a short shot in the paint when he was undercut by a stumbling Al Horford of the Hawks with 8:33 left in the first quarter.
Randolph, an All-Star last season, fell hard on his right lower back. He limped off the court during a timeout, then returned to make two free throws.
But he struggled down the court on defense and asked to be taken out with 8 minutes left in the quarter. He walked to the locker room with medical staff.
He came back into the game and scored four points on 1-of-6 shooting, but he appeared to have trouble jumping for shots and rebounds. He did not return for the second half and was replaced in the lineup by Sam Young. The Grizzlies said Randolph had a lower back contusion.