A near-complete roster turnover among the Lions' CB corps this year may offer the unit a chance to improve their pass defense, but it hasn't eliminated the injury issues that plagued the secondary late in the 2011 season.

CB Chris Houston (ankle) and S Louis Delmas (knee) were held out of Wednesday's practice. Coach Jim Schwartz said neither player would see action Sunday if he didn't practice during the week. Since Friday workouts are traditionally not run at full speed, Delmas and Houston are likely to be doubtful for Sunday's game if they don't participate in the Lions' full-speed practice Thursday.

If Houston is unavailable, it's likely that rookie CB Bill Bentley will see significant playing time as part of a rotation with Drayton Florence, Kevin Barnes and Jacob Lacey. Bentley's experience with the Lions in camp also gives him an edge to start over Barnes and Florence, who are new arrivals. For most rookies, the prospect of starting a game against the Rams' former No. 1 overall pick Sam Bradford would be a daunting prospect, but Bentley says he's ready for the challenge.

“It would be an honor and a blessing to be out there with the starting unit for all the hard work I'm putting in,” he said. “I want to be tested [by Bradford]. It gives me an opportunity to make plays and get a couple of spotlights.”

Bentley's play during training camp -- including an interception during Detroit's preseason opener -- certainly proved he has the ability to grab the spotlight he covets, but his aggressive coverage style also saw him get beaten for several big plays. He says his preseason experience has helped him learn how to walk the line between playing aggressively and playing recklessly.

“You've got some situations where you can be aggressive, and some where you know you can't be aggressive,” he said. “You've got know when to play within your scheme.”

Whether he starts or not, Bentley will have one eye on a familiar face on the St. Louis sideline Sunday. He was a teammate of Rams' second-round pick Janoris Jenkins at Pahokee, Fla. high school.

Bentley said he remains friends with Jenkins but that the pair's friendship would be placed on hiatus during Sunday's game.

“We can't be friends on the field at all,” he said. “It's about being friends before and after the game, and loving each other.”

Rookie Riley Reiff working at LT: Reiff took second-team left tackle reps during position drills Wednesday. The switch to left tackle is noteworthy, because Reiff saw time at RT for large portions of training camp. Lions coaches are confident that Reiff can handle either tackle position, but his switch to the left side during drills reaffirms the assumption that Reiff is being groomed as the heir apparent to veteran tackle Jeff Backus.

WR Broyles improving during drills: Despite seeing limited action during training camp, WR Ryan Broyles' performance in drills Wednesday appears to have affirmed Lions' coaches confidence that he would be ready for action when the regular season began. Broyles is cutting well following the completion of a lengthy ACL rehab process, and he moved without hesitation during position work. Detroit didn't list him on its injury report, which means he was a full participant in the team drills portion of practice that is closed to media. Absent a setback in practice this week, Broyles should be ready to go for Sunday's game.

Lions make practice squad change: Detroit signed safety Ricardo Silva to the practice squad Wednesday and released cornerback Ross Weaver. Silva was released from the Lions' active roster Monday to make room for cornerback Drayton Florence. His remaining practice squad eligibility made him one of the few members of the secondary that Detroit could release without severing ties completely with the player. He spend the majority of the 2011 season on the Lions' practice squad before being elevated to the active roster late in the season when injuries decimated the defensive backfield.

Follow Lions reporter John Kreger on Twitter at @CBSSportsNFLDET and @JohnKreger.