On the day of their final open-to-the-public training camp practice, the Steelers pulled a roster move that pleasantly surprised many of their fans.

Pittsburgh activated RB Rashard Mendenhall and NT Casey Hampton from the PUP list Friday.

While Hampton's removal from the PUP was seen as being immanent in the next two weeks, Steelers general manager Kevin Colbert told 93.7 The Fan in Pittsburgh last week he anticipated Mendenhall would begin the season on the PUP list.

Players who are on the PUP when the regular season begins cannot play the first six weeks of the season.

Mendenhall's right knee was injured Jan. 1 at Cleveland and Hampton's left ACL was torn Jan. 8 in the playoff loss to Denver. After the move was announced Friday, Colbert told 93.7 The Fan the team wanted to give Mendenhall -- a two-time 1,000-yard rusher -- and Hampton -- a five-time Pro Bowler -- every chance to get themselves ready to play when the regular season begins Sept. 9 at Denver.

"It's a great feeling to have everybody coming back," backup NT Steve McLendon said. "Hampton has worked out every day on the field. People don't see the side I see of Casey I do. He's an extremely, extremely hard worker and I'm very excited for him to return and do what Casey does."

The Steelers host theIndianapolis Colts on Sunday. Neither Mendenhall nor Hampton will play, but they are expected to practice Tuesday when workouts resume at the team facility in Pittsburgh. Mendenhall could wear a "noncontact" jersey.

Tackle Max Starks, for example, came off the PUP list this week but during his first practice Friday was limited and did not participate in team drills. Colbert, Steelers coaches and teammates have been raving about the development of McLendon, a former undrafted player who has improved to the point there was little -- if any -- drop-off with him at nose tackle in Hampton's stead.

But the Steelers surely will welcome back Hampton, their first-round pick in 2001 who has 157 games of NFL experience.

"I wish I could say I can be as dominant as Casey," McLendon said. "He's extremely powerful, he's strong, and for a big guy, he's quick."

Mendenhall's not the only running back in pain.

Running back John Clay and FB David Johnson have been lost to season-ending injuries, and Jonathan Dwyer had a shoulder injury that kept him from practicing earlier this week. Dwyer is expected to play Sunday.

The depth at the position has been so tested that there were practices earlier this week in which Baron Batch and rookie Chris Rainey were the only halfbacks available. Neither has played in a regular-season game.

It's possible the situation helped nudge the Steelers' hand into making the PUP move with Mendenhall. 

Follow Steelers reporter Chris Adamski on Twitter @CBSSportsNFLPIT and @BuzzsawPGH.