SANTA CLARA, CA - SEPTEMBER 14: Cornerback Kyle Fuller #23 of the Chicago Bears runs back an interception against the San Francisco 49ers at Levi's Stadium on September 14, 2014 in Santa Clara, California. (Photo by Ezra Shaw/Getty Images) Kyle Fuller runs back an interception against the San Francisco 49ers in 2014. (Ezra Shaw/Getty Images)

By Dan Durkin–

(CBS) After participating in joint practices this week in Indianapolis, the Bears and Colts line up for their second dress rehearsal Saturday night at 6:30 p.m.

Here are a few players and position battles to focus on.

Cornerback Kyle Fuller

After his strong start last season, Fuller’s play took a precipitous drop. Starting with the Packers game in Week 4 of 2014, opponents made him the mark in the passing game, and he didn’t hold up. Fuller was targeted twice in the preseason opener against the Dolphins, and both passes were completed for a total of 30 yards.

The Bears were primarily a zone-based coverage scheme under previous defensive coordinator Mel Tucker. Under new defensive coordinator Vic Fangio, they’ll play more man coverage, specifically press man with their outside cornerbacks. Fangio runs mixed and hybrid coverage schemes that will require Fuller to hold up on an island with less safety help over the top.

The Colts present a Packers-like passing attack. They’re led by Andrew Luck, the game’s premier young quarterback, and a bevy of receivers who can win with both straight-line speed (T.Y. Hilton and Phillip Dorsett) as well as size and leverage (Andre Johnson and Duron Carter).

It’s not an exaggeration to say the success of the secondary is predicated on Fuller’s development as a true No. 1 cornerback, so he must take a step forward on Saturday night.

Right tackle competition

Jordan Mills’ poor performance against the Dolphins didn’t go unnoticed by the Bears’ offensive coaching staff. Second-year prospect Charles Leno got first-team snaps at right tackle during Thursday’s joint practice against the Colts.

Leno got snaps as a rookie in the team’s sixth offensive lineman personnel grouping. He has ideal length, but he’s struggled with speed on the edge. The Colts are searching for edge pressure, so you should key on Leno when he’s matched up against Colts outside linebacker Erik Walden in pass protection sets.

The Bears need someone to step forward at the position. The most logical solution would be to move Kyle Long outside, but the coaches seem content to leave him at guard at the moment.

It’s clear the new coaching staff sees Mills’ deficiencies, and their patience may be running thin waiting for corrections. His inability to hold up in singles (one-on-one blocking assignments) on the edge has a cascading effect on personnel groupings and the number of eligible receivers out in routes.

Monitor who lines up and gets the most run with the first team. John Fox has never been hesitant to move parts around in order to get the best five blockers on the field.

Marquess Wilson and the No. 3 WR in 11 personnel

With receivers Kevin White (shin) out indefinitely and Alshon Jeffery (calf) out for Saturday’s game, Wilson should get plenty of opportunities and targets. What he does with them remains to be seen.

Last preseason, Wilson was looked upon to complement leverage players like Jeffery, Brandon Marshall and Martellus Bennett with a speed element. A broken collarbone shelved him for half of the season. This preseason, the tables have turned for Wilson.

Last week, the Bears opened the game in 11 personnel, in which Wilson joined Eddie Royal and Marc Mariani. Cutler targeted Royal three times and Wilson once. As expected, there were miscommunications on a few routes, which needs to be cleaned up as the preseason progresses.

Even when Jeffery returns, Wilson projects to be on the field for more than half of the team’s offensive snaps, given coordinator Adam Gase’s preference for three-wide packages. He also projects to see a lot of single coverage. He’s a long-armed hands-catcher with some quickness and open-field vision but must translate his physical skills into reliable route running and yards after the catch.

Pay attention to who lines up as the third receiver with the first team in their 11 personnel grouping. Could it be a player like undrafted rookie Cameron Meredith?

The injuries to White and Jeffery have paved the way for Wilson and others to earn more snaps and targets, so who will make the most of the extra opportunities?

Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter @djdurkin.