Watson has been battling appendicitis and missed practice Wednesday and Thursday as doctors tried to decide whether surgery was necessary. Watson has been able to avoid that for now and returned to practice Friday, but the Saints decided he would be inactive for Sunday.
The team listed Watson as questionable Friday.
If surgery is necessary, it would be a tight turnaround for Watson to play in the Super Bowl, should the Saints make it. If the Saints don't advance to the Super Bowl, then Watson's final game will have been last week against the Eagles in the divisional round of the playoffs.
Watson, 38, has announced that this will be his final season in the NFL. A first-round pick for New England in 2004, Watson has also played for the Browns and Ravens. This is his second stint with the Saints.
Keith Kirkwood, who caught a key fourth-down touchdown pass in last Sunday's win over the Eagles, has been ruled out of Sunday's game with a calf injury.
ESPN's Mike Triplett contributed to this report.