LATROBE - Pittsburgh Steelers coach Bill Cowher tried to baby his top three running backs through the early portion of training camp, but the team has lost one for a month.

Duce Staley underwent surgery Monday to repair a lateral meniscus tear in his right knee. Cowher expects him to miss a month, but isn't worried about Staley's health in the long run.

"He felt good about what took place when he came out," Cowher said. "We're hopeful to have him by the opening of the season."

Staley practiced only once with the team before fluid built up in his knee. He rested three days and tried to practice Saturday, but didn't feel comfortable and decided to have it examined. The MRI revealed the tear Sunday.

Cowher said he believes that the injury occurred at training camp, since team trainer John Norwig traveled to South Carolina to check on Staley while he was training at home.

The injury thrusts Jerome Bettis back into the role of starter. He finished last season as the first-team halfback after Staley injured his hamstring during the Halloween game against New England.

Bettis rushed for more than 100 yards in six of the eight games he started and finished the season with 941 yards on 250 carries.

"I'm ready to go to work," Bettis said. "That's what I do. I didn't come back to be able to carry it 50 times. My goal was to come back, and if I was going to come back to be able to go if they needed me, and right now it looks as though they need me."

Bettis, 33, who ranks fifth on the all-time rushing (13,294) list and third on the all-time carries (3,369) list, admits to feeling his age.

"Now I've got to get rest, get to bed, get iced, I've got to do all those things, a lot of preventive things I never used to do," he said. "It's so funny because I used to see all the older guys get the ice after practice, and do this, and stretch all the time. I'd just fly into the training room, grab a toothpick or something and, boom, I'm gone. But now, I find myself 30 minutes after practice, 45 minutes after practice, 40 minutes before practice, and I say to myself, 'Wow, I'm one of the old guys now.'"

Bettis will likely give way to younger runners Verron Haynes, Willie Parker and rookie seventh-round pick Noah Herron throughout much of the preseason.

Haynes, though, has struggled with injuries throughout his three-year career. His 2003 season was cut short by knee surgery and his rookie season was ended by a fracture fibula. Last year, Haynes served as the team's third-down back and gained 272 yards rushing (4.8 avg.) and caught 18 passes for 142 yards. He was excused from the run test this year because of the injury history with his knee.

Haynes appeared healthy during the goal-line drill Saturday. Lining up with the first team, he ran once for a yard before breaking off a 4-yard touchdown run.

Cowher wouldn't reveal any plans he may have for a backfield rotation, but Haynes said he believes the solution's simple.

"You stick to what got us to where we needed to be last year," he said. "Jerome was the guy and I came in on third downs and when he needed a breather. I don't see that changing."

Notes:

Wide receiver Lee Mays (hamstring), defensive end Travis Kirschke (low back) and outside linebacker Clark Haggans (flu) missed practice. ... Linebacker Alonzo Jackson missed the morning practice, as well as Saturday's practice, to be with his girlfriend for the birth of their daughter, Zoie. ... The Steelers came to camp with an open roster spot and filled it Monday with the signing of running back Chad Scott, a former backup to Parker at North Carolina.