JACKSONVILLE – If the ones aren't done, they're close to it.

That's NFL preseason reality after Preseason Week 3 – and that's the Jaguars' reality as they prepare for their 2017 preseason finale at Atlanta Thursday.

What's done is pretty much done. Starters are unlikely to play much Thursday, if at all. That's the NFL norm, and although Head Coach Doug Marrone won't likely rule many starters and or front-line players out, neither are they likely to play nearly as much as in Preseason Weeks 1-3.

So, where does that leave a few key areas as the regular-season opener against the Houston Texans approaches? September 10, after all, now is two weeks away.

Glad you asked. Because you did, here are three key unknown areas – and the accompanying concern level around each – as the Jaguars prepare to play the Falcons at Mercedes-Benz Stadium in Atlanta Thursday night in the 2017 preseason finale:

1) Defense, particularly defensive front.This wasn't supposed to be a major issue, and there's every chance it won't be come the regular season. The Jaguars were the NFL's sixth-ranked defense last season, and a big reason was the front seven was typically stout against the run. The unit added end Calais Campbell and the following players either left via free agency or were released: end Tyson Alualu, tackles Sen'Derrick Marks and Roy Miller and linebacker Dan Skuta. The worry in preseason: the first unit's performance early against opponents' front-line quarterbacks and offenses. New England didn't play starters in Preseason Week 1, but Tampa Bay and quarterback Jameis Winston and the Carolina Panthers and quarterback Cam Newton started the past two games driving too easily against the Jaguars' first unit. The absence of cornerbacks such as Jalen Ramsey, A.J. Bouye and Aaron Colvin hasn't helped, but defensive players have talked after the last two games about needing to start faster. They're right. Concern level:Not overly high. This unit has too much experience, speed and talent to keep starting so slowly.

2) Injuries.This is always a preseason area to watch, and at first glance it's a concern with players such as running back Leonard Fournette, wide receiver Marqise Lee, Bouye, Colvin, running back T.J. Yeldon, tight end Mychal Rivera, wide receiver Dede Westbrook and defensive end Dante Fowler Jr. missing Preseason Week 3 against Carolina Thursday. Ramsey missed the first two weeks of the preseason and played one series Thursday. So, how are the Jaguars on the injury front? That's tricky because Marrone doesn't reveal many specifics, but the sense is that the Jaguars thus far are in good shape. Long snapper Carson Tinker (torn anterior cruciate ligament) is the lone front-line player/starter out for the season. Lee, Fournette, Fowler, Bouye, Colvin, Westbrook and Ramsey are practicing this week. It remains to be seen how much they will play against Atlanta, if they play at all. Concern level:Low. The No. 1 preseason goal is to emerge healthy and be full-go Week 1. The Jaguars have a very real chance to be close to that goal.

3) Offensive line.Other than quarterback (and goodness knows, we've talked quarterback enough in recent days), this is the No. 1 area of concern as the preseason closes. Three starting spots have appeared relatively settled for weeks: right tackle Jermey Parnell, right guard A.J. Cann and center Brandon Linder. Marrone has been hesitant to name rookie Cam Robinson the starting left tackle, but despite Robinson giving up an early sack against Carolina Marrone said Saturday he liked how Robinson responded – and that he's comfortable with the idea of Robinson starting the season. Guard is a less-settled issue. Patrick Omameh started the first two preseason games at left guard, Luke Bowanko started Preseason Week 3 and Marrone said the team is still trying to figure out who to start at the position. Cann struggled against the Panthers with three penalties and too much penetration allowed, but Marrone has said nothing about a move there. More concerning than the details of each starting position overall has been the run blocking in general. Jaguars running backs rushed for 30 yards on 17 carries against Tampa Bay and other than a 51-yard run on a fake punt by Corey Grant, they rushed for 56 yards on 22 carries against Carolina. Marrone also cited quarterback Blake Bortles' ability to extend plays as a reason for choosing him as the starter. Concern level: High. The preseason does not define the regular season, and the return of Fournette should help the run game. Still …