Leftwich is expected to return to the 53-man roster on Monday. He already is guaranteed his full salary this season.
Leftwich, mending from a left knee injury, was not expected to play against Tennessee. The Steelers will go with Dennis Dixon and Charlie Batch at quarterback, as they did in their opener, a 15-9 overtime win over Atlanta.
With nose tackle Casey Hampton (hamstring) injured, the Steelers were down to two backup defensive lineman. Leftwich's roster spot will be taken by Steve McLendon, a first-year player from Troy State.
Leftwich was expected to start during Ben Roethlisberger's suspension, but he injured his knee on Sept. 2.