The first off-day is Sept. 20, which will be dividing line of sorts. Here are 5 storylines to watch during camp:

Over the first six days of training camp, there will be two split-squad practices, preseason games on four successive days/nights starting on Sunday plus corresponding morning skates for players involved in the games and separate practice sessions for those who aren't playing.

1. THREE C

Unlike last year, when there was a variety of jobs and roles up for grabs and a host of rookies broke camp with the team on the opening-night roster, there are only a couple of spots up for grabs entering this year's camp. However, things can change if there are injuries or based on extremes of camp performance for the better or worse.

One definite spot up for grabs: third-line center. The departure of veteran Valtteri Filppula during the off-season opened a battle for the center role in support of Sean Couturier and Nolan Patrick. Ideally, the Flyers would like to cultivate a third line that can also score with some regularity but also plays a responsible 200-foot game. Accomplishing that feat starts down the middle.

GM Ron Hextall has cited several potential in-house candidates to fill the role vacated by Filppula. He has mentioned Jordan Weal (primarily a winger in the NHL to date, but a successful offense-generating center at the American Hockey League level), Scott Laughton and veteran Jori Lehtera (if he'd slide up from fourth line center to third).

Two players who were members of the AHL's Lehigh Valley Phantoms last season are also candidates: second-year pros Mikhail Vorobyev and Mike Vecchione.

If none of these options pan out in camp, the Flyers may look at trade options. Hextall said outside options were considered over the summer but none arose whom he viewed as clearly superior to the in-house returnees or farm system promotional candidates.

In the meantime, highly regarded 2017 first-round pick Morgan Frost, who is too young to play in the AHL this season, would need a spectacular NHL camp with the Flyers to win the third-line center spot at age 19.

2. FILLING IN FOR A-MAC

Prior to the news that Flyers alternate captain Andrew MacDonald would miss approximately six weeks (including the first few weeks of the regular season) due to a lower-body injury suffered in an off-ice workout, the Flyers' blueline seemed relatively set heading into camp. Now, there is a battle for a spot in the starting six.

One option is righthanded-shooting defenseman Christian Folin, whom the Flyers signed to a one-year contract this summer as an unrestricted free agent. He brings size, some physicality and shot blocking as well as NHL-level penalty killing experience.

Second-year pro Philippe Myers is his primary competition for a starting-six spot to open the season. Myers is also righthanded and brings an arguably more dynamic skill than Folin. However, the 21-year-old Myers is still navigating various aspects of the professional learning curve after missing much of the first half of his rookie Phantoms season due to injury. Overall, Myers came on strong in the second half and Calder Cup playoffs last season.

Hextall has stated that he prefers young players not to sit out long stretches of time as healthy scratches, if avoidable. He'd prefer a prospect to play regularly in the AHL level instead. Thus, if Folin beats out Myers in camp for a starting-six spot to open the season, the role of seventh defenseman could be claimed a player such as veteran Phantoms defenseman T.J. Brennan. In addition to winning two Eddie Shore Awards (the AHL equivalent of the Norris Trophy), Brennan has 53 games of NHL experience.

3. STAY HEALTHY THROUGHOUT

Injuries are a factor that is beyond any team's control and can spring up at any time. Injury issues can significantly change the shaping of the opening-night roster, such as with the effect of MacDonald's injury. It should go without saying that the Flyers hope to be as healthy as possible as they pare down the roster in camp and then set their opening-night roster, but there's only so much that can be done to avoid the injury bug.

There is some good news on the Flyers injury front: top-line center Couturier and veteran power forward Wayne Simmonds are right on schedule to engage in partial participation in the early portion of training camp and then play in a couple of exhibition games in the latter portion of camp. Ditto goaltenders Brian Elliott and Michal Neuvirth.

If either Elliott or Neuvirth have a setback or sustain a new injury during training camp, Alex Lyon is the most likely first-in-line candidate to be promoted from the Phantoms to the Flyers to open the season on the NHL roster. Top goaltending prospect Carter Hart will likely need some AHL seasoning before he becomes a call-up candidate. Veteran Anthony Stolarz, who appeared in a handful of NHL games for the Flyers in 2016-17, is on the bounceback path after missing nearly the entire 2017-18 season due to a recurring knee injury that previously held him out of the 2017 Calder Cup playoffs.

4. THE DARK HORSE & BUBBLE CANDIDATES

Almost every year, there are players who are not often mentioned as roster candidates before camp who step up either to win opening-night spots or at least lay the groundwork for in-season recalls. One name to keep an eye on as a potential in-house penalty killing forward option is versatile Phantoms veteran Corban Knight. A younger dark horse could be energetic and agitating forward Cole Bardreau.

A Flyers regular starter as a rookie in the first half of last season but a frequent healthy scratch in the second half, Taylor Leier is a bubble candidate for this year's opening night roster. If he does not make the opening night roster, Leier would be subject to waivers before he could be assigned to the American Hockey League. Veteran Dale Weise, another incumbent, also faces competition for his roster spot.

5. EARLY CAMP vs. LATER CAMP

Due to the slew of early-camp games, the sheer number of players in camp in the early going and the typical nature of the preseason (i.e., veterans and roster locks play sparingly early in camp, with young players and bubble players getting more time) do not expect much opportunity for systems reinforcement and special teams work during the early portion of training camp.

During the latter portion of camp, with the roster being whittled down and veteran regulars getting more work in leading up to opening night, there will a much greater emphasis on structural play and special teams.

It's no secret that improving on the penalty kill is a primary goal for the Flyers in the upcoming season. That storyline, however, really isn't one that will start to play out in earnest until the season begins. As a rough estimate, the Flyers are aiming to pull themselves at least closer to the middle of the NHL pack on the PK with a success rate north of 80 percent. Additionally, the team hopes to foster a more productive second power play unit to accompany an already potent and proven first unit.