Also placed on injured reserve was tight end Jerame Tuman, who has been out a month with a back injury. Neither Clark nor Tuman can play again this season.
Center Marvin Philip and cornerback Grant Mason were signed from the Steelers' practice squad to replace Clark and Tuman on the 53-man roster. Philip, a sixth-round pick last year, was cut during training camp this year and has spent the season with the practice squad.
Clark has an inflamed spleen that was detected as the Steelers played at Denver on Oct. 21. He was forced to stay behind in Denver for a night before rejoining the team, and has not played since.
Anthony Smith, a third-round pick from Syracuse in 2006, has taken Clark's place in the lineup.
Copyright 2007 by The Associated Press