Agassi, 34, said he has an injured right hip. Nalbandian said Sunday that he injured his knee and would likely miss the event.
Agassi and Nalbandian both lost in the final of their most recent tournaments. Agassi lost a three-straight decision at the Stockholm Open. Nalbandian lost to Jiri Novak in a five-set final at the Swiss Indoors.
Neither players will qualify for the season-ending Masters Cup.
The Masters Cup begins in Houston on Nov. 15, with only eight players selected from the ongoing ATP race. Agassi was in eighth place and Nalbandian in ninth, but neither had clinched a berth. Gaston Gaudio, who is 10th, automatically qualifies because he won the French Open this year.