The Detroit Lions are hours from the official start of the league year and while the franchise has not made any big moves in the pre-free agency period, they do have holes to fill on their roster.

While the largest gaps are on defense, the Lions have many areas that need upgrades -- so here's a look at what the Lions' defense looks like heading into free agency.

Defensive end: Starters -- Ezekiel Ansah; Jason Jones. Backups -- George Johnson (RFA tendered); Darryl Tapp; Devin Taylor; Larry Webster; Phillip Hunt; Roy Philon; Kerry Hyder.

Thoughts: A bit of a logjam already at the position, the only way the Lions make a move here is if someone snags Johnson from them. The other option could be kicking Jones inside, but that seems unlikely.

Defensive tackle: Starters -- TBD. Backups -- TBD; Caraun Reid; Jermelle Cudjo; Xavier Proctor.

Thoughts: The biggest need the Lions have right now, the Lions have no starting tackles and don't even have a No. 3 rotational tackle. The Lions will have to make some moves here in free agency and will probably add to that in the draft as well. Ndamukong Suh is gone. The Lions missed an opportunity last season by passing on drafting Aaron Donald. Nick Fairley, C.J. Mosley and Andre Fluellen, for now, remain free agents. A lot of work needs to happen here. Terrance Knighton, Vince Wilfork, Henry Melton, Corey Peters, Ahtyba Rubin and Dan Williams could be potential options here.

Linebackers: Starters -- Tahir Whitehead (SAM); Stephen Tulloch (MIKE); DeAndre Levy (WILL). Backups -- Kyle Van Noy; Travis Lewis; Julian Stanford; Jerrell Harris.

Thoughts: The only way Detroit makes a move here is if there is a schematic switch to a 3-4, but even then, Tapp and Hunt have played linebacker in that system. The Lions have a bunch of talented players here and if they do add a linebacker or two, it'll be more focused on special teams instead of actually contributing to the defense. Next year will be something to pay attention to here as Levy, Whitehead and Lewis enter the final years of their deals, and Tulloch will have an unfriendly $7.3 million cap number in 2016.

Cornerback: Starters -- Darius Slay (outside); TBD (outside); Bill Bentley (nickel). Backups -- Nevin Lawson; Crezdon Butler; Mohammed Seisay.

Thoughts: The Lions need to add at least one cornerback during free agency -- be it re-signing Rashean Mathis or going in a younger direction. In addition, this is probably an area where Detroit drafts a cornerback somewhat early, especially if the Lions retain Mathis for one more season. Nickel should be covered with Bentley and Lawson but there could be a scenario where the team re-signs Mathis, adds another starting-caliber corner and kicks Mathis inside for slot work.

Safety: Starters -- Glover Quin; James Ihedigbo. Backups -- Don Carey; Nate Ness.

Thoughts: Detroit is probably not chasing a starter here -- at least not an immediate one. Ihedigbo is in the last year of his deal, though, so that could be something to watch in the future. Don't be surprised if there is a safety added here as a primary special teams contributor. Isa Abdul-Quddus would be a good fit to re-sign. If he doesn't, perhaps the Lions take a look at Sergio Brown, who has some starting experience along with strong special teams capabilities.

Specialists: Matt Prater (K); Sam Martin (P); Don Muhlbach (LS).

Thoughts: These spots are set, but the Lions will likely sign a kicker and punter at some point in free agency just to rest Prater and Martin's legs during camp.