By Dan Durkin-

(CBS) In back-to-back weeks, the Bears have found themselves lining up with rookies in the secondary in passing situations to close out one-possession games. Against the Jets on Monday, the Bears had three rookies in the defensive secondary, yet in the end, they made plays to preserve a victory.

Each week affords a finite amount of practice time, most of which is catered toward getting the starters prepared. Regardless, safety Ryan Mundy said that defensive coordinator Mel Tucker is emphasizing that it’s a “next play” mentality for everyone on the roster.

“Even before last week, coach Tucker came in the defensive meeting room and said our job is to make sure everyone in this room is ready to play,” Mundy said. “Because at some point during the season, you’re going to have to step on that field and make a play for us.”

The challenge for Tucker then becomes ensuring that every player who is active for the game — regardless of their role entering the game — has a grasp of the game plan and can execute should they be called upon.

“The guys that are on the roster, particularly guys that are up for the game, they understand the game plan,” Tucker said. “They know what to do with the defensive calls. It’s just a matter of recognizing who is down and who the backup is and getting them out there. Then just making sure that everything on the call sheet, they can execute. We make sure they are up on the game plan and they can perform. You really don’t have time to do anything else other than get them in there and call the next play and let’s go play.”

Brock Vereen was drafted to play safety but displayed coverage versatility at Minnesota, lining up as a slot corner, field corner, boundary corner, box safety and a free safety. Versatility is a popular word within the Bears’ personnel department, and it has been on display over the last two weeks for Vereen. Against the 49ers, he was thrust into the slot corner role, and against the Jets he was back at safety.

“In the San Fran game, some of the techniques we asked him to play in the nickel spot were some similar techniques that we ask him to play as a safety,” Tucker said. “We huddled up on the sideline and decided what are the calls that have carryover for him and those are the calls that were available to us and those are the ones that we called.”

Vereen defended Jeremy Kerley on the Jets’ final fourth-down play that iced the game for the Bears.

Fellow rookie Kyle Fuller has turned heads around the league. His performance against the 49ers earned him NFC Defensive Player of the Week honors, and his play during the regular season isn’t coming as a surprise to his coaches and teammates. He leads the NFL with three interceptions, including a pick of Geno Smith in the end zone Monday.

“He stepped in Day 1 and made plays in practice,” Tucker said. He’s going to be where he’s supposed to be in the defense most of the time, and that’s going to allow him to have opportunities to make plays for us. He’s fundamentally sound and he plays hard defensively. He’s got a great awareness. He’s a team guy. To the best of his ability, he’s gonna be where he’s supposed to be. I think that’s what you’re seeing out there.”

Linebacker Lance Briggs said that Fuller is being looked at by teammates to not only play his role but also to be a playmaker on defense.

“Now that the season’s in, he’s made some big plays in big games,” Briggs said. “Those are impact plays. There’s a chance the Jets could have scored points. We take six points off the board that never get on the board. He’s a guy that when you do stuff like that now, you set a standard for yourself. We’re now going to rely on you to be an impact player week in and week out.”

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