Harrison has been sidelined since spraining the medial collateral ligament in his right knee during the Patriots' final regular season game with Tennessee. He missed six regular-season games because of a broken shoulder blade.
The 13-year veteran missed 13 games in the 2005 regular season and the team's playoff games last season because of torn ligaments in his left knee.
During the 2006 regular season, Harrison had 34 sacks, 15 assists, one sack, one fumble recovery and an interception.
New England also said wide receiver Troy Brown missed Wednesday's practice because of the flu and was listed as questionable for Sunday's game.
The Patriots travel to Indianapolis for a game with the Colts Sunday, with the winner advancing to the Super Bowl Feb. 4.