Vikings starting safety Harrison Smith will not play in Sunday's game against the Atlanta Falcons because of a left knee injury.

Smith missed the first two practices of the week but was able to do some work Friday, giving the Vikings hope that he could be ready to face the Falcons in Atlanta. But the team said Saturday that he will be scratched.

Smith's likely replacement will be second-year player Antone Exum. It would be his first NFL start.

Smith was injured last week against Green Bay on a fluke play. A forward pass slipped out of the hand of Packers quarterback Aaron Rodgers and bounced twice toward cornerback Terence Newman. A second later, Newman lunged for the ball in case it was a fumble and collided with the extended leg of Smith, who was casually reaching to pick up the ball.

Smith has a team-leading 54 tackles and one interception.

Rookie cornerback Trae Waynes (ankle) also will not play.

STaff, wire reports