Saints head coach Sean Payton said Monday that McKenzie will have surgery this week and be placed on injured reserve.
Later in the day, the Saints claimed recently released Washington cornerback Leigh Torrence off of waivers, giving him McKenzie's roster spot.
Coming back from a right knee ligament tear late in 2007, McKenzie sat out the Saints' first two games of the regular season, but played in the past seven and started six.
He had an interception and was credited with 22 tackles and three passes defended before his latest injury occurred during a 34-20 loss in Atlanta on Sunday.
Torrence, who is 5-foot-11, 179 pounds, is now in his third NFL season. Waived by the Redskins on Saturday, Torrence has played in 35 career regular-season games, starting once.
Torrence played in Washington's first nine games, making nine tackles as a reserve defensive back along with 11 tackles on special teams.
The Saints have now lost two starting cornerbacks this season. Rookie Tracy Porter was placed on injured reserve after dislocating his wrist during a Week 5 loss to Minnesota.
Meanwhile, reserve cornerback Aaron Glenn reaggravated a left ankle injury in Atlanta. Payton said it was not yet clear how long Glenn might be out, but noted before the addition of Torrence that the only three healthy cornerbacks on the roster were Randall Gay, Jason David and Usama Young.