Cause for concern: Top 2011 NFL Draft prospects all have red flags

The day Andrew Luck announced he was going back to Stanford, the top of the 2011 NFL Draft became far less certain. The field is loaded with talented players, but they all have red flags. Here's a closer look at the issues that are giving teams pause as the draft approaches:

PRINCE AMUKAMARA, CB, NEBRASKA

Red Flag: Not tough mentally; no interceptions his senior season.

Amukamara can explain the lack of interceptions by claiming defenses avoided him all year. But look at the highlights of Amukamara's matchup with Oklahoma State's Justin Blackmon. They didn't shy away from throwing at Amukamara, and the few times he did got beat, he had trouble recovering.

DA'QUAN BOWERS, DE, Clemson

Red Flag: Junior year was far more productive than rest of his career; injury concerns.

If Bowers could fight off double-teams and total 15.5 sacks his junior year, why did he have only four sacks combined in his freshman and sophomore seasons? Injuries were a contributing factor, and those questions have emerged again for the talented pass-rusher. SI.com's Peter King reported in his Monday column that Bowers failed at least two team physicals on his knee at the combine. The defensive end will have many questions to answer at Clemson's pro day Friday.

MARCELL DAREUS, DT, Alabama

Red Flag: Didn't dominate in two seasons at Alabama (66 tackles, 11 sacks combined).

Dareus' role was to fill gaps and occupy blockers at Alabama. But some wonder if he took plays off and if he's explosive enough to merit one of the top three picks in the draft. Don't even bother comparing him to last year's No. 2 pick, Ndamukong Suh, who appears to be a once-in-a-decade type of defensive tackle.

NICK FAIRLEY, DT, Auburn

Red Flag: One-year wonder; not a hard worker.

Fairley has gained a reputation as having a soft body during the lead up to the draft, possibly because his workouts are limited by a shoulder injury he suffered during the season. That might be OK if he had a larger body of work teams could evaluate, but he doesn't.

BLAINE GABBERT, QB, Missouri

Red Flag: Played in a spread offense at Missouri; put up pedestrian numbers (16 TDs, 7 INTs) last season.

Sam Bradford probably made Gabbert some money by proving quarterbacks could transition quickly from a spread offense to the pro game. But even in what is traditionally a quarterback-friendly system, Gabbert had only three games with 300 or more yards passing. Chase Daniel put up record numbers at Missouri, but he was throwing to future NFL receivers, while Gabbert didn't have many weapons.

A.J. GREEN, WR, Georgia

Red Flag: Slight build; high 4.5 in the 40.

Green is not going to strike fear into the hearts of defenses like the Lions' Calvin Johnson does. He's not fast enough to burn teams downfield. And he won't be able to out-physical cornerbacks like the Texans' Andre Johnson can. Those are lofty comparisons -- Johnson and Johnson are tough to match -- but if Green goes as high as some people have projected, he had better be at least close.

JULIO JONES, WR, Alabama

Red Flag: Doesn't get separation; drops passes.

Jones blew everyone away with a 4.39 40 at the combine, but he doesn't play to that speed on the field. He made some tremendous catches in traffic, partially because he doesn't create enough space between himself and the defender. And he had some mental lapses, dropping easy balls and coasting against defenses he should have crushed.

VON MILLER, OLB, Texas A&M

Red Flag: Small for a linebacker; didn't put up big numbers against top competition.

Miller is 6-foot-2½, 237 pounds and will play a position where players are usually 6-4, 250-260. Can he stop the run? Does it matter if he gets after the quarterback like he did at Texas A&M? Some scouts have doubts about how Miller matched up with elite offensive linemen in college.

CAM NEWTON, QB, Auburn

Red Flag: Played in a spread offense; scrambling quarterbacks don't project well into the NFL.

Throw out all the scrambling he did at Auburn, because that doesn't fit the prototype for success in the NFL. Teams are more focused on his ability to run a pro offense. Coaches who don't have a lot of time to develop a guy -- like Buffalo's Chan Gailey -- may consider Newton too risky.

PATRICK PETERSON, CB, LSU

Red Flag: Too big to be a shut-down cornerback.

Peterson reportedly got down to 212 pounds for the combine, but will play around 220 next season -- and he's not going to get smaller as he physically matures. He can't match fellow draft prospect Prince Amukamara's cover skills. Peterson might end up being a very good NFL safety, which could be disappointing to a team that takes him in the top five, as the shelf life on safeties is less than that of cornerbacks.

TYRON SMITH, OT, USC

Red Flag: Didn't play left tackle in college.

Smith has a good chance of being the first tackle taken, but he might need some time to develop. A team taking him in the top 10 would probably want to plug him right into the line, even if he's not ready.