LATROBE - The Pittsburgh Steelers' two-man running back rotation was missing both of its main components in practice Saturday, and Duce Staley's sore right knee is becoming a concern.

Staley missed most of the second half of last season with a sore right hamstring - allowing Jerome Bettis to nearly get another 1,000-yard season - and he has sat out all but one full day of training camp contact work because of the aching knee.

Staley underwent an MRI test Sunday to make sure there's nothing wrong.

"We'll kind of go from there, see where he's at," Steelers coach Bill Cowher said. "He still doesn't feel real comfortable."

Staley needed fluid drained off the knee after just one day of practice, a condition that sometimes can indicate a problem that requires arthroscopic surgery. With the regular season more than a month away, Staley has enough time to have an operation and still be ready for the Sept. 11 opener against Tennessee.

"We're going to be very proactive, make sure if there's any problems to get them taken care of now because we want him ready to go for the first game," Cowher said.

Bettis, who finished up last season with a minor quadriceps tear, also sat out Saturday, mostly just so he would have two days off in a row before a full week of camp next week.

Staley took part in some light running, but skipped the offense-vs.-defense goalline drill Cowher traditionally uses to wrap up the first week of camp. The offense twice gets the ball at the 5-yard line and has four plays to score.

Just as a year ago, when new offensive coordinator Ken Whisenhunt was determined to re-establish the running game after a season's flirtation with a passing-heavy offense, all the plays were runs.

But, unlike a year ago, the offense needed just two plays to score twice, on a 4-yard run by Verron Haynes and a 5-yard run by Willie Parker. Last summer, the defense halted eight consecutive runs without allowing a score, yet Whisenhunt still felt he set the tone for the season by calling eight consecutive power running plays.

After the worst rushing season by a Steelers team since the late 1960s while going 6-10 in 2003, they Steelers again were the NFL's top rushing team a year ago with 2,464 yards. They ran the ball 61 percent of the time, easily the most lopsided run-to-pass percentage in the league.

"We were going to run it" on every play Saturday, Whisenhunt said, even if it meant extending an already long practice. "We talked about it before practice, and they said, 'We don't expect anything different.' I said, 'Look, if you guys want to get out, just get it in early. It was good to see that."

Parker's run showed off the speed that kept him on the roster a year ago as an undrafted rookie free agent from North Carolina. He couldn't find a hole inside, but bounced it outside to his left and got across the goal line.

"He certainly gives you a little bit of a speed option," Whisenhunt said. "It's exciting when he gets into the open field and he's doing a good job with his inside running.

Parker was a backup as a college senior, rushing for only 181 yards, but had more than that last season (186 yards) as an NFL rookie. With Staley and Bettis both out of the regular season-ending game at Buffalo the Bills needed to win to make the playoffs, Parker - then No. 4 on the depth chart - ran for 102 yards on 19 carries in a 29-24 victory.

"I think the thing is you feel comfortable about putting him in there," Whisenhunt said. "Last year, we thought good about him in the preseason but once we got into the season, that's different. Now, you feel more comfortable."

Notes:

Undrafted rookie free agent LB Andre Frazier, who stood out in several drills, and TE Walter Rasby had the first fight of camp, exchanging punches during a blocking drill. ... QB Ben Roethlisberger took off on a 25-yard scramble during a passing drill. ... Just after Haynes scored, Bettis walked toward the defense and yelled, "That's how we do it." ... Character actor Bill Nunn, the son of Steelers scout Bill Nunn, attended camp for the first time in more than 20 years. He was a team ballboy 35 years ago. Nunn has been in films such as Spider-Man, New Jack City and Do The Right Thing.