St. Louis Rams running back Steven Jackson will miss at least one week with a partial tear of his left groin, an injury sustained in the fourth quarter of Sunday's 24-3 loss at Tampa Bay. Rookie Brian Leonard, a second-round pick from Rutgers, will get his first start Sunday at Dallas. Coach Scott Linehan said Jackson would be week to week. The 0-3 Rams learned they lost Jackson a day after guard Mark Setterstrom was lost for the season with a torn left knee ligament and cartilage damage. Setterstrom is the second lineman the Rams have lost this season, after seven-time Pro Bowl tackle Orlando Pace injured his shoulder in the opener. Linehan said Jackson, who had 115 yards on 30 carries, was hurt making a cut. He said Jackson stayed in the game for a while after being hurt but said it was "noticeable" that Jackson was injured.