Rookie Peyton Hillis, who had energized the offense over the last month, on Monday became the fifth Broncos tailback to go on injured reserve when medical tests showed he had a torn right hamstring behind the knee and could need surgery. He faces a two-month recovery.

The Broncos are now down to their seventh tailback in Tatum Bell.

Hillis had moved over from fullback with the spate of injuries to the Broncos' battered backfield and was the biggest surprise among a dozen rookies who are getting significant playing time in Denver this season.

He averaged 5.0 yards a carry and scored five times, including an 18-yard rumble Sunday before getting hurt in Denver's 24-17 win over Kansas City that put the Broncos (8-5) on the brink of the playoffs.

Hillis rushed for 343 yards and had 179 yards receiving with one touchdown catch. He quickly emerged as a fan favorite by running over safeties and bullying his way past first-down markers and the goal line alike.

"It's always tough to lose a guy like that," coach Mike Shanahan said. "But he will be good for the future. He's proved that he can play tailback in the National Football League, and that one catch he made was probably as good a catch as you could make in a very tough situation and unfortunately, he pulled his hamstring making that catch."

Hillis, who rushed eight times for 58 yards, made an acrobatic, leaping catch but when he landed, he was smothered by free safety Jarrad Page and cornerback Brandon Carr. Hillis was bent in half with his right foot planted and his right knee straight.

Shanahan said Hillis suffered a 2- to 3-inch tear of his right hamstring.

Hillis joins tailbacks Andre Hall, Michael Pittman, Anthony Alridge and Ryan Torain on IR. Plus, Selvin Young, the starter when the season began, has carried just once in the last two months because of a torn groin.

"It's disappointing you lose him at this time of year because he's a load and he's one of the few guys ever that I've watched that will actually run over safeties," Shanahan said of Hillis, a seventh-round draft pick from Arkansas who made his mark in college blocking for first-round draft picks Darren McFadden and Felix Jones.

The Broncos will promote Cory Boyd from the practice squad to compete with P.J. Pope to serve as Bell's backup.

Bell, who was selling cell phones at a local mall when he was re-signed last month, had a 28-yard run on Denver's winning 95-yard touchdown drive Sunday. He's rushed for 100 yards on 24 carries since his return to Denver, where he played from 2004-06.

After a dismal season in Detroit, he was jettisoned by the Lions and went to work hawking cell phones and wireless plans at a kiosk at the Aurora Mall before the Broncos came calling again last month.

"Well, when he's gotten his opportunity to play, he's played well," Shanahan said. "And he made a guy miss on that one sweep, and he did a nice job and got some big yards on that play. So, I've been pleased with him."

Taking advantage of his second chance, Bell has adjusted to the Broncos' offense faster than expected for somebody coming in at midseason and having been out of football and working 9-to-5.

"I think anytime somebody's out on the streets for a while, everybody gets humbled," Shanahan said. "If a coach has been fired, a player that's been cut, it's the same thing. You look forward to those opportunities and you take advantage of those opportunities once you get them.

"And Tatum's come in, worked extremely hard and he's taken advantage of an opportunity."

The Broncos' troubles at running back present a unique opportunity for Bell, who played three solid seasons for Denver and gained 1,025 yards rushing in 2006 to re-establish himself as an NFL back.

Bell has at least one supporter in receiver Brandon Marshall.

"We've got T-Speed back there," Marshall said. "Hillis has been doing a great job, and that's the only thing keeping Tatum on the sideline. He's a premier back in this league, and I'm excited to see what he's going to do."

Notes

If Hillis finishes the season as the team's leading rusher, his 343 yards will be the lowest leading total in team history. Gerald Willhite's 347 yards in the strike-shortened 1982 season is currently the low. ... Boyd, who was signed to the Broncos' practice squad on Nov. 4 after being waived by Tampa Bay in July, said he's caught on quickly to Denver's offense because he ran in a similar offense at South Carolina. ... Shanahan said WR Brandon Stokley (heel) should be able to play on Sunday at Carolina. Stokley was still limping and looked to be in a lot of pain when he walked gingerly through the locker room Monday.