Although neither player will need surgery to repair knee injuries, the Pittsburgh Steelers will be without two key starters this weekend, when the team faces the Baltimore Ravens on Sunday.

Steelers officials on Wednesday officially listed tailback Jerome Bettis and center Jeff Hartings on the leaguewide injury report as "out" for the contest. Coach Bill Cowher originally felt the players would be listed as "doubtful," but that was overly optimistic.

Fourth-year veteran tailback Amos Zereoue and second-year center Chukky Okobi will each start their first regular-season games.

Hartings suffered cartilage damage to his left knee while pass-blocking in the second half of the Monday night victory over Indianapolis. Bettis got off to a strong start, scoring two first-half touchdowns in the game, and then he departed with a sprained medial collateral ligament in his left knee.

It is not yet known how much time either player will miss. The game in Baltimore is for first place in the AFC North, as both the Steelers and Ravens have 3-3 records.

Len Pasquarelli is a senior writer for ESPN.com.