McAllister suffered the torn right knee ligament in last Sunday's 52-3 loss to Green Bay. An MRI on Monday revealed the tear, but he has yet to have season-ending surgery.
In five games this season, he ran for 335 yards and three touchdowns and had 17 receptions for 117 yards.
On Tuesday, the Saints traded a future conditional draft pick in 2006 to the Miami Dolphins for running back Jesse Chatman to fill McAllister's roster spot. They also have waived cornerback Fred Booker and signed safety Siddeeq Shabazz, who has played in 26 career games for Atlanta and the Oakland Raiders.
The 5-foot-11 inch, 200-pound Shabazz spent the 2005 pre-season with the Washington Redskins. He was a seventh round draft choice by the Raiders in 2003 out of New Mexico State.