By Chris Emma–

INDIANAPOLIS, Ind. (CBS) — Two days shy of their second preseason game, the Bears have some shuffling on their first-team offensive line.

Before leaving practice with an apparent calf injury, Jordan Mills was working with the second-team unit at right tackle, while Charles Leno saw reps with the first team. Coach John Fox wouldn’t commit to Leno over Mills for the preseason game against Indianapolis.

“He’s been playing with the twos all of camp, and he’s been performing well,” Fox said of Leno.

Entering his third year with the Bears, Mills has started 29 games to this point. However, he’s faced great struggles during this preseason. That was on display during Chicago’s first preseason game, as Mills seemed to scuffle.

In his place, the Bears are trusting Leno, the second-year player out of Boise State. Leno started one game and played in six during his rookie season of 2014 and has stood out enough to catch the eye of Fox.

Will it be Leno over Mills for Saturday’s contest at Lucas Oil Stadium? That’s a decision to be decided in part by evaluation and also with Mills’ health status.

“We haven’t even met as a staff yet,” Fox said after Thursday’s practice. “That’s something I need to talk to them first on.”

Lucky test

Traveling down to Indianapolis for joint practices with the Colts was a decision the Bears made in order to mix up the preseason routine.

After a while, teammates grow tired of hitting other teammates, practices can become stale and the energy needs a boost. But changing the opposing personnel is one thing. Going up against one of the best quarterbacks in football is another. Andrew Luck is a challenge for the Bears to battle.

“I love going against Luck,” Bears safety Antrel Rolle said. “I think he’s definitely one of the best quarterbacks in this league. He’s very wise beyond his age.”

Luck showed his best abilities during a two-minute drill in which he drove the Colts to a six-play, 80-yard scoring drive, finishing it by finding T.Y. Hilton in the corner of the end zone.

The Bears were better in Thursday’s practice following a struggle Wednesday, but it’s difficult to slow down Luck.

“It was a good look and a good test,” Bears cornerback Tim Jennings said.

In a daunting schedule, the Bears will face plenty of great quarterbacks. There are games against Aaron Rodgers, Russell Wilson and Peyton Manning, among others.

Getting a player with the caliber of Luck out of the way during the preseason is a helpful measuring stick. Of course, the Bears already knew he was good.

“He’s a hell of a quarterback,” Rolle said.

Mentoring Rolle

Rolle is an 11-year NFL veteran who has experienced a lot during his NFL career. He’s lining up next to Adrian Amos, the rookie out of Penn State who’s going through his first NFL preseason.

So the veteran leadership of Rolle is undoubtedly something that can be of benefit for Amos. The two are working well together in the Bears’ secondary.

“He’s definitely learning quickly,” Rolle said of Amos. “He’s a smart guy, catches on to the defense really well, he has a high-level skill set, so that’s only going to help him out.”

Amos found his way to the Bears’ first-team defense this week, in advance of the second preseason game. Brock Vereen was bounced back down to the second-team unit.

With this move for Amos, he must establish a connection with Rolle, the free-agent signing who’s learning the Bears’ new defense.

“It’s really going to be about the communication and how we gel together at safety,” Rolle said. “So far, we’ve been doing pretty well.”

Extra points: Linebacker Pernell McPhee left practice early with an apparent injury … Linebacker Jared Allen was excused from practice for a veteran’s day off … Cornerback Tracy Porter and Daniel Thomas were among notable players missing practice due to injuries … The Bears hold a private walk-through practice Friday before their game Saturday.

Follow Chris on Twitter @CEmma670.