PITTSBURGH — Willie Parker has begun an NFL season as a virtual unknown, as a 1,000-yard running back, as a Super Bowl star and as one of the league’s best running backs.

Never has Parker gone into any season as one of two running backs sharing a job, as he and Rashard Mendenhall likely will do for the Pittsburgh Steelers this season.

Not unexpectedly, Parker is uncertain what to expect four days before the Steelers’ first game.

Will he get as many carries as usual? Or far fewer? Will he get the ball near the goal line, or will he come off the field? Do the Steelers still look at him as the running back who will get the ball when games are ready to be won, as coach Mike Tomlin said he does?

The three-time 1,000-yard rusher, coming off an injury-interrupted season, is unsigned past this season, and that creates another unknown.

Namely, is he still the Steelers’ primary running back, or is Mendenhall being groomed

– and quickly – for that job?

A hamstring injury limited Parker to four carries during the preseason, yet Tomlin said he remains the feature back in one of the NFL’s most run-heavy offenses. Since the NFL merger in 1970, the Steelers have rushed for more than 5,000 yards more than any other team.

“Willie Parker is our runner,” Tomlin said. “He (Mendenhall) is going to get an opportunity to get his touches. But more importantly than anything else, Willie Parker is our runner.”

Parker was held below

1,000 yards for the first time in four seasons as a starter last season – 791 yards on 291 carries – while being bothered by knee and shoulder injuries over the final three months and the playoffs.

Parker hopes what Tomlin is saying is true, but he also knows the Steelers didn’t draft Mendenhall in the first round a year ago to sit him.

He also does not know where he’ll be playing next season.

“Right now I’m the guy, and me and Rashard are doing a two-back system so we have to help each other out and keep this running game going,” Parker said Sunday as the Steelers began practicing for Thursday night’s NFL season opener against Tennessee.

Two backs, one football. It’s a system that’s become increasingly popular in the NFL as teams try to maintain running games with backs whose skills complement each other. With the Steelers, the 28-year-old Parker is the speed back and Mendenhall a power-type inside runner.

Mendenhall, whose own 2008 season ended with a severe shoulder injury in late September, showed flashes during the preseason, but apparently not enough to convince the Steelers he should get the majority of carries.

Mendenhall carried 32 times for 99 yards, a touchdown and a 3.1 average, yet rookie Isaac Redman – signed Sunday to the Steelers’ practice squad – was the team’s leading rusher.

Also returning to the Steelers as practice squad players were center A.Q. Shipley, a seventh-round draft pick from Penn State; defensive tackle Steve McLendon, running back Justin Vincent, tight end Dezmond Sherrod, linebacker Donovan Woods and wide receiver Tyler Grisham.

Defensive end Sonny Harris, a sixth-round draft pick, was claimed by Carolina.

“Willie will be just fine, he’s a great running back, but we’ve also got some great running backs who can fill the void if necessary,” quarterback Ben Roethlisberger said. “That’s what’s special about this offensive group is we’ve got a lot of guys who we can fill in with.”

No matter who gets the ball, he will have a different lead blocker in front of him.

Carey Davis, the Steelers’ primary fullback the last two seasons, was waived and tight end Sean McHugh went on the injured reserve list following knee surgery and is done for the season. McHugh essentially served as a fullback when he played last season.

“We got a two-back system now, so when they call my number I just got to be ready,” said Parker, who averaged 304 carries and 1,337 yards per season from 2005-07. “Coach Tomlin told me 30 carries (per game), but I don’t know about that. I’ve just got to be ready.”

Linebacker Lawrence Timmons (high ankle sprain) didn’t practice Sunday, a sign he might not be ready for Thursday’s game. Timmons, a first-round pick in 2007, moved into the lineup this season after Larry Foote left to play for Detroit.