Defensive end - With the Lions trading George Johnson to the Tampa Bay Buccaneers, there is a spot up for grabs at defensive end. In all likelihood, Devin Taylor and Larry Webster will see an increased role to fill that spot in the rotation, but it wouldn't be all that shocking if the Lions end up drafting a pass rusher. They could take one in the first round if a top defensive end falls to the 23rd overall pick, or they could add another developmental player later in the draft. In any case, this is a position where the Lions could look to add even more depth and talent despite already being in decent shape.
Defensive tackle - Ndamukong Suh and Nick Fairley are gone and C.J. Mosley and Andre Fluellen are unsigned, leaving the Lions with a brand-new top four at defensive tackle in 2015. Haloti Ngata and Tyrunn Walker are set to be the starters, but a lot is unsettled at this position. The Lions have Caraun Reid, Jermelle Cudjo and a few others looking to break into the rotation, but they really need to upgrade their depth via the draft. That could mean taking a starting-caliber player in the first round or selecting someone on Day 2 who will add some extra depth and take some time to develop into a starter. Or, perhaps the Lions will wait until Day 3 to add another body to the position and look for immediate help elsewhere. Regardless of what route they take, defensive tackle has to be addressed in some form before the 2015 season.
Linebacker - This may be the deepest position on the Lions' entire roster. They've got one of the best 4-3 outside linebackers in DeAndre Levy, a proven veteran returning from a torn ACL in Stephen Tulloch and an up-and-coming player set to return to strongside linebacker in Tahir Whitehead. They also have guys like Josh Bynes and Kyle Van Noy, who will hopefully develop into future starters, and several other players who can contribute on defense and special teams. All of this is a long way of saying that linebacker is set. There's a lot of talent and depth at this position, and although I suppose you can never say never when it comes to the possibility of the Lions drafting a linebacker, there isn't exactly a need here.
Cornerback - On paper, the Lions' starters are basically set at cornerback. Darius Slay and Rashean Mathis will continue to be the starters on the outside, and Bill Bentley should return to his nickelback role if he's healthy. The Lions also have Nevin Lawson, Josh Wilson, Mohammed Seisay and Crezdon Butler providing additional depth. In the short term, this position appears to be in decent shape, but the Lions need to start thinking about life after Mathis considering he will be 35 in August. Ideally, they would add a cornerback in one of the early rounds and spend 2015 developing him into a starter. It'd also be nice to get better at the nickel spot, but the Lions really need to put their focus on finding someone to eventually take over for Mathis.
Safety - Assuming James Ihedigbo's contract dispute doesn't linger and he does in fact play for the Lions this season, this is another position that appears to be in decent shape in the short term. Glover Quin was a Pro Bowler last season, and Isa Abdul-Quddus is an excellent backup option, so between those two players and Ihedigbo, the safety position is in good hands. However, with so much uncertainty surrounding Ihedigbo and him turning 32 in December, the Lions should start thinking about his eventual replacement. Perhaps Abdul-Quddus will ultimately step into that role, but if the right situation presents itself, I could see the Lions taking a safety pretty early in the draft this year. It wouldn't even shock me if they take a safety in the first round if Landon Collins is still on the board. This isn't exactly a pressing need, but it will be in the future if the Lions don't take a proactive approach at safety.