PITTSBURGH — The Pittsburgh Steelers know they can't keep running Willie Parker 29 times per game, like they did in their opener. What they don't know is who should succeed the retired Jerome Bettis as the big running back who can wear down defenses and keep Parker rested.

Duce Staley tried out for the role but, despite still being on their roster, couldn't win the job after averaging 2.2 yards per carry during the preseason. Patrick Cobbs was the next to audition, getting a quick look following a productive camp with the Patriots, only to be cut by the Steelers.

Next up is former Packers running back Najeh Davenport, who spent the last four seasons in Green Bay — much of that time in the trainers room. The 250-pound Davenport has been productive when he's been healthy, but injuries kept him out of 29 of the 64 games he spent with the Packers.

"He's a proven big back," Steelers coach Bill Cowher said. "We were kind of looking for that. He's played third down and fullback, and that gives you some flexibility. ... He was the one guy out there who fit what we were looking for with the makeup of our roster."

What Davenport must show the Steelers is he can stay healthy. He hasn't played in a regular-season game since breaking his right ankle in Green Bay's fifth game in 2005, after scoring two touchdowns against New Orleans earlier in the game. He missed a combined 16 games in 2004 and 2005, the equivalent of a full season.

What the Steelers like is he was productive when he was on the field, averaging 4.9 yards on 217 carries. That's even better than Parker's 4.8 average through 24 career games.

"I like the big-back thing," said Davenport, who is eager to move into that role with the Super Bowl champions. "Being a big back, I went to (the University of) Miami because they had James Stewart, so I'm just a big fan of the big-back system."

Parker, coming off a 1,202-yard season, is expected to get more carries inside an opponent's 20-yard line — and in the second half — than he did last season, when much of his production came on first and second downs. He added about 15 pounds during the offseason to help him become a stronger runner, but the Steelers still don't want to wear down the fastest running back in club history.

"I don't want to give Willie 30 carries every game," Cowher said. "Last year he had 22 in the first game and 25 in the second game and then we started backing him down some. It's got to be something we monitor and see how he feels."

One curious note: the Packers chose to keep former Northwestern back Noah Herron when they released Davenport. Herron was a Steelers seventh round draft pick last year and spent much of the season on their practice squad.