Clooney had been scheduled to travel to New York Sunday for appearances on shows including "Good Morning America," "The Daily Show" and "Charlie Rose," his spokesman, Stan Rosenfield, said Monday.
But Clooney told Rosenfield on Saturday that his condition had worsened and he would be unable to travel. Rosenfield said he didn't have information on how or when the injury occurred.
The former "ER" star, whose sequel to the caper film "Ocean's Eleven" opens Dec. 10, was being treated by a doctor, Rosenfield said. He declined to provide details.
Asked when Clooney, 43, might be back on the publicity trail to talk about the movie, Rosenfield said, "Hopefully next week."
"Ocean's Twelve" co-stars Julia Roberts, who gave birth to twins, a boy and girl, on Sunday.