Although the injury isn't considered serious -- see Brian Urlacher's four-day, nonissue knee injury -- when Bush or Forte aren't on the field, the battle for No. 3 RB comes under closer scrutiny. The leader may not be the person it figured to be before the start of camp.
Kahlil Bell started in the No. 3 spot after gaining 337 yards on 79 carries when Forte got hurt and Marion Barber had fumblitis. But Armando Allen has had more reps with first or second team than Bell and provides a different look as more of a third-down or "scat" back at 5-foot-10, 190 pounds.
"I think my skill set is that I'm very versatile," Allen said. "Being that I am the smallest back that we have, I think maybe I can get into the open field and do a couple things.
"All of our backs are great, but me being small and fast are things I think I can use to my advantage to help the team."
Allen (Notre Dame) played in two games last year for the Bears and had 48 yards on 15 carries, including a 13-yard run against Green Bay. But he didn't get to show his true strength, which is catching the ball out of the backfield.
At camp, Allen has often caught passes far downfield like a WR rather than dump-offs like most backs do. Allen had 119 catches for 833 yards and three scores at Notre Dame.
"I definitely won't downplay the look that I got last year," Allen said. "I think it was definitely an opportunity that I had to showcase my talent and let them see what I had."
When Allen hasn't been on the field, former Viking Lorenzo Booker has also taken snaps from Bell. Booker, in particular, has been targeted for special teams. He has been returning kicks with Eric Weems still sidelined with an ankle injury.
Positioning: Although rookie TE Evan Rodriguez has been a crowd favorite in Bourbonnais, drawing applause with catches downfield, he remains entrenched as the fourth TE. Kyle Adams, the second-year player from Purdue, is the third TE playing with Matt Spaeth and Kelvin Davis when the Bears go to a three-TE formation. It will be interesting to see if the Bears decide to keep the fourth-round draft pick or a player (Adams) who showed promise last year before suffering a hamstring injury. ... Harvey Unga was a RB coming out of BYU in the supplemental draft two years ago, and it now apears his days of being a ball carrier are over. The Bears have been lining him up at FB, as the backup to starter Tyler Clutts. He has been catching some passes out of the backfield, particularly in shotgun formation. ... Tackles Gabe Carimi (right side) and J'Marcus Webb (left side) took all the first-team snaps with Chris Williams relegated to backup at RT and rookie undrafted free agent James Brown handling backup LT. ... Julius Peppers sat out practice with unspecified soreness. He had a knee problem that plagued him last year off and on.
Frey Day: Rookie CB Isaiah Frey (5-11, 190, Nevada) made the INT of camp by tipping the ball into the air and snaring it with one hand Sunday. Frey, a sixth-round pick, has been a little more noticeable on defense than seventh-round CB Greg McCoy of TCU. But McCoy's return abilities have been showcased on special teams. Both are hoping to get onto a crowded CB list at cutdown time but may have to unseat veteran Jonathan Wilhite or Kelvin Hayden to do it.
Full house: Olivet Nazarene officials set the crowd for Sunday's practice in excess of 12,000.
Follow Bears reporter Gene Chamberlain on Twitter: @CBSportsNFLCHI.