But now, with Mr. Kanak entering the picture, the eventual outcome is becoming a little harder to predict. Analysts at Morgan Stanley said in its research note that they still believe Mr. Sullivan has the inside track, but "this latest move does add more uncertainty to that potential outcome."

Mr. Kanak, 50, who replaces Edmund Tse in the co-chief operating officer role, has been serving as president and CEO of AIG Companies in Japan and Korea.

Morgan Stanley observed that Mr. Kanak, educated both in the United States and England, is well regarded within the company for having led strong growth in the company's Japanese and Korean life operations.

The fact that Mr. Kanak has been leading AIG's Asian life units could turn the succession decision in his favor, since Asian life insurance is becoming AIG's strongest long-term growth potential business. "Mr. Kanak's past experience carries significant weight," said Morgan Stanley analysts.

The timing of Mr. Greenberg's retirement or management change could also swing the succession decision to either candidate. If the change were to occur soon, Mr. Sullivan is still the stronger candidate, Morgan Stanley hypothesized. But if Mr. Greenberg were to stay around longer, Mr. Kanak could gain the edge, as the company's growth plan in Asia takes hold.