Pittsburgh, PA -- (Sports Network) - The Pittsburgh Steelers have ruled out All-Pro safety Troy Polamalu for Sunday's game against the Chiefs.

An MRI exam earlier this week revealed the Steelers safety has a strain of the posterior cruciate ligament. The injury is to his left knee, the same knee that cost him four games earlier this season due to an MCL sprain.

Polamalu left this past weekend's 18-12 loss to Cincinnati during the Bengals' first drive of the game and did not return. He made one tackle before leaving, although it wasn't clear if that is where the injury occurred.

In five games this season, Polamalu has three interceptions, 20 tackles and seven passes defended.