Harrison has experienced swelling in the knee since the spring and has not practiced during training camp. He is on the physically unable to perform list.
Harrison, 34, had nine sacks in 11 games last season. He is in his ninth NFL season, all of them spent with the Steelers, and he signed a five-year contract extension this year.
There was no indication when he might return to action.
2014: The Year in Music [PHOTOS]