Reed hasn't played since Baltimore's last meeting with the Steelers on Nov. 29. He's struggled with both foot and groin ailments for the past month.
Ravens starting left tackle Jared Gaither also is doubtful for Sunday with a foot injury.
This is a big game for both Baltimore (8-6) and Pittsburgh (7-7). The Ravens currently hold the fifth seed in the AFC and can control their own playoff destiny with two wins to finish the regular season.
Pittsburgh, the defending Super Bowl champions, needs to sweep its final two games and receive help from other teams.
James Walker covers the AFC North for ESPN.com.