Lions GM Martin Mayhew said change is coming to Detroit's roster. (US Presswire)

After Detroit’s 10-6 season in 2011, GM Martin Mayhew used the limited salary cap space he had to ensure that the core of the Lions team that earned the franchise’s first playoff berth this century remained intact.

One year later, Mayhew isn’t happy with what he calls a “disappointing” 4-12 record. That means several players could be looking for work.

“There is a possibility [of major roster change] there,” he said. “One of the reasons that we wanted to get everybody back [after the 2011 season] was because we were coming off a season where we had success. Obviously, coming off this season, we want to take a look at everything that we’re doing from a front office, coaching, and player standpoint.”

Mayhew wouldn’t comment when asked about specific players’ shortcomings, but he made it clear that he believed Detroit’s defense was responsible for the majority of the team’s issues this season.

That assertion isn’t a surprise coming from Mayhew, who was a Super Bowl-winning cornerback during his playing days. He has always prided himself on trying to assemble a solid defensive unit, and said this season’s group -- which allowed an average of 27 points and 341 yards per game -- fell short of the mark.

“Who on our defense played better than they did last year?” he asked. “Probably Ndamukong [Suh] … Of the 10 defensive starters we brought back, probably Ndamukong is the one that played noticeably better. Some guys flat-lined and some guys were either injured or didn’t play as well… we didn’t get the individual performances that make the unit better.”

The individual performances Mayhew is talking about have nothing to do with work ethic or technique. In fact, he says he’s satisfied with the way Lions’ defenders practiced and prepared throughout the season. What the Lions were missing, Mayhew says, were game-changing plays and turnovers that can give teams a crucial field-position advantage as well as vital momentum.  

“The turnover ratio [minus-16] is really out of whack,” he said. “We scored seven touchdowns on defense in 2011. We had none this year. That’s a huge difference in the way that our games went. We’ve got to get back to being that kind of defense.”

To return to the defensive form that helped the Lions make the postseason last year, Mayhew says he will look to add players to the roster that bring more to the table than a solid knowledge of the game -- including bolstering a secondary that was by far Detroit’s weakest unit.

“We need impact players, especially on the back end on the defense,” he said. “We’ve got a lot of guys that line up right and know what their job is, but they don’t impact the game. We need interceptors, we need guys that sack the quarterback, we need guys that cause fumbles and make plays on third down. Those are the kind of guys that can change the game for us.”

Adding new talent could be difficult because of Detroit’s tight salary cap situation, and it's also worth noting that the Lions’ top two defensive backs -- safety Louis Delmas and cornerback Chris Houston -- are unrestricted free agents this season. Mayhew says he’s confident that the team will be able to add enough talent to the roster to improve the defensive backfield despite the salary cap concerns, and he says he’s not afraid to part ways with any player -- even established starters -- that he doesn't see as part of his vision for 2013.

“It’s not about money, it’s about performance,” he said. “Guys that performed well this season are in a different situation than guys who didn’t perform as well. When you win four games, you’re looking [to replace] your underperformers.”

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