BOURBONNAIS, Ill. -- The Chicago Bears held out linebacker Lance Briggs (rest) for Thursday's practice, thrusting rookie second-round pick Jon Bostic -- who was filling in for injured middle linebacker D.J. Williams -- into the role of playcaller on defense.

Bostic drew positive reviews for his first day making the calls.

"He did very very well," defensive end Julius Peppers said. "We're going to need him. We hope Lance doesn't go down, but he could. All of us could go down. So whenever somebody goes down, the next player has to be up. So we've got to get him ready because we might need him one of those games."

The Bears could wind up needing Bostic sooner than originally anticipated. The club drafted Bostic with the expectation he would spend 2013 learning behind Williams, a 10-year veteran, who at one time was considered one of the NFL's most talented middle linebackers. Williams suffered a strained right calf on Wednesday, and the prognosis given by the team has been "week to week," which means the injury could linger.

"I really don't look at it as getting thrown in the fire," Bostic said. "I'm out there with a lot of guys I've pretty much watched on TV the last 10 or 12 years, however long I’ve been watching football. To be in there with them, I’ve got to pick it up. I've got to go out there and make sure I'm in my playbook off the field so I'm not making any mistakes when I'm out there."

Here are some observations from Thursday's workout at Olivet Nazarene University:

• One theme in the first six practices has been the slow start on offense in the opening team period. Thursday was no different. Quarterback Jay Cutler started off 1-of-3 passing with two of those throws deflected at the line of scrimmage.

• A rash of injuries on the offensive line forced J'Marcus Webb to return to an old spot: left tackle. Webb also lined up at right tackle at times during practice, flip-flopping sides with Eben Britton on the first team. Kyle Long played primarily with the starters at right guard.

"Our goal is to find the best five," offensive coordinator Aaron Kromer said. "When we find the best five, it'll be obvious. Whether we put them at left guard, right guard, whoever they are, we'll find them. And we don't control when that'll happen. It'll just happen."

• The offense heated up as the workout progressed with Cutler connecting with Marshall on a deep ball down the sideline despite tight coverage from cornerback Charles Tillman.

• Luckily, Tillman isn’t tackling Marshall at practice.

"I think if we were tackling hard in practice, I'd be going to the NBA or something, because I wouldn't be playing this game," Marshall joked. "I tried that during the lockout, and that didn't go well. I stepped out there and tried to shoot a 3, airballed it, and said, 'Let me stick to football.' "

• Tight end Martellus Bennett made several long receptions down the middle of the field in both 7-on-7 and 11-on-11, including one grab requiring that forced him to twist around his entire body. Six-foot-six hybrid tight end Fendi Onobun also found the end zone on a long completion from Cutler, thanks to a busted coverage by strong safety Major Wright.

• Cornerback Sherrick McManis popped tailback Armando Allen on a running play, while safety Tom Nelson laid out tight end Gabe Miller on a short sideline route. Both hits were clean, but might have indicated the Bears are reaching the stage of camp where players become tired of hitting one another and tempers occasionally flare on the practice field.

• Receiver Joe Anderson made a nice diving catch falling out of bounds on a throw from quarterback Josh McCown. One of Anderson's competitors for a roster spot, wideout Devin Aromashodu, continued to produce a solid camp after signing with the Bears late in the offseason.

"I know the quarterbacks have a confidence level in (Aromashodu) because they've been around him (in the past)," Bears coach Marc Trestman said. "They know him a little bit better than the coaches do. He understands what's going on, has played here, played the position."

• Long nearly chased down second-year safety Brandon Hardin who was attempting to run the length of the field for a score after stripping away the ball. Hardin eventually pulled away, but not before Long displayed speed not typically associated with an offensive lineman of his size.

"I just kind of put my head down and started running," Long said. "I saw which direction he was going and I tried to get a good angle on it; just trying to save a touchdown. You don't want turnovers to turn into touchdowns. That's something they preach here. We're going to show some speed here."

• Bostic and veteran James Anderson worked as the nickel linebackers with Williams (calf) and Briggs (rest) not in uniform.

• According to camp officials, attendance Thursday was approximately 7,500 for an estimated camp total of 37,500.