The Boston Celtics are heading into the 2015-16 season with competitive rebuilding in mind, but springing back to title contention will take time.

While the Celtics' aggressive rebuilding approach started off on an awe-inspiring track, the master plan turned into a perplexing puzzle last summer. Boston failed to draw the interest of top free agents and was forced to settle for the remaining breadcrumbs.

Celtics President of Basketball Operations Danny Ainge initially maneuvered through the trenches of rebuilding better than expected. He flipped his aging veterans for future draft picks and young assets while keeping the salary sheet clean. Ainge's approach wasn't all too different than that of the deplorable Philadelphia 76ers, yet Boston still managed to clinch the seventh seed in the Eastern Conference with a 40-42 record last season.

Boston remains positioned to pounce at the next disgruntled superstar who may or may not become available. However, until that day arrives, this roster is likely stuck in the dreaded purgatory of the NBA—contending for a postseason spot yet lacking the upside to really challenge the top dogs.

The Celtics have a lot of interesting pieces already in place, and watching the young core grow under the competent guidance of head coach Brad Stevens promises to be a pleasant experience. But until Boston discovers a lead dog for its sled, it's journey projects to be a bumpy ride.

Key Additions/Subtractions

• Additions: David Lee (trade), Amir Johnson (free-agent signing), Perry Jones (trade), R.J. Hunter (drafted), Terry Rozier (drafted), Jordan Mickey (drafted)
• Subtractions: Brandon Bass (signed with Los Angeles Lakers), Luigi Datome (signed overseas), Phil Pressey (waived), Gerald Wallace (traded)

Clearly, Lee was the summer's biggest addition to the roster, as the Celtics decided to swallow his expiring $15.5 million deal in a trade with the Golden State Warriors. His presence appears redundant on paper, especially considering the logjam at power forward. He is also the oldest player on the roster at 32, which makes it hard to envision him as part of the big-picture plan.

While Lee, who is coming off a championship run with the Golden State Warriors, has every reason to be disgruntled with the move, he seems to have embraced his role. Lee organized a players-only dinner early in preseason in Milan and seems keen to lead the young group by example.

"It’s the nice part of a trip like this," Lee said, via Mauro Bevacqua of the Boston Herald. "Nobody brought their families or friends, it’s just us over here, so little things like this one are very important as a way to come together as a team."

Lee will essentially replace the departed Bass, although he'll have to share minutes with the newly acquired Amir Johnson. Last year's starter at power forward, Jared Sullinger, will also compete for playing time, but he might see his role slightly decreased in light of the recent additions.

Storylines to Watch

The Celtics will remain in stasis within the East until they make a trade splash or reel in a major free agent, but that doesn't mean this team isn't comprised of compelling storylines.

This year could determine which players will remain key cogs in Boston's future plans. There are only a few players on the roster who have established firm identities in the NBA, while others are in the process of figuring theirs out.

Watching the likes of Marcus Smart and Kelly Olynyk make strides in their young careers will be intriguing. Smart could potentially evolve into the third-best player on a championship-contending roster, while Olynyk's versatile offensive skill set remains an alluring factor.

Stevens has a lot of decisions to make as far as his rotation goes, especially in the frontcourt. There are 96 minutes up for grabs at power forward and center, and Boston theoretically has five players who should play between 20 and 30 minutes across those positions. That's not even including Jonas Jerebko's playing time or any potential small-ball experiments with Jae Crowder or Perry Jones at the 4.

It's difficult to single out one player whose efforts could swing the pendulum in the right direction, simply because the pecking order on offense is still ambiguous.

Avery Bradley will remain not only the starter but one of the most important players on the team. His development plateaued last season, and there is a decent chance that he simply is who he is five years into his career. However, if he can make another leap forward, the Celtics could have one of the league's scariest backcourts in a couple of years.

Bradley isn't much of a playmaker, but there isn't overwhelming pressure for him to be one. Smart will be running the show, and Boston can slot excellent passers into just about every other position. But if Bradley can rehabilitate his three-point shot, which dipped to 35.2 percent last season, and attack the rim with more conviction, things could get interesting. He is getting to the line just 1.2 times per game so far in his career.

Lineups featuring Isaiah Thomas and Smart functioned surprisingly well last season. In the 228 minutes the backcourt duo shared on the court, the Celtics outscored opponents by a whopping 12 points per 100 possessions, according to NBA.com. Going to that pairing brought greater balance to Boston on both ends, as Thomas made up for Smart's shaky playmaking.

Bradley logs more minutes than either of those guards, which makes his improvement that much more crucial.

Bradley himself isn't shy when setting personal goals, and while he might have plans to contend for accolades in defensive categories, he senses that there is plenty of room for improvement offensively as well, according to Jay King of MassLive.com:

"For sure making the All-Defensive team," Bradley said. "I would even love to get Most Improved if I continue to work and keep getting better, and prove what I can do on the offensive end. I think a lot of people kind of push that to the side, but I feel like the last few years – obviously I could have been better – but I feel like I've had a pretty consistent couple of years. If I can keep it going and even take it to another level, I feel like I can be in the talk for that as well."

Making the Leap

With just one player (Lee) over the age of 28 on the roster, there is plenty of breakout potential across the board. For someone to truly make the leap, several prerequisites have to be in place. The player has to have an inherently high ceiling but also be presented with room and opportunity to grow.

All the requirements seem to be in place for Smart. He has already secured the starting job, and the 27 minutes per game he logged during his rookie campaign are bound to increase to at least 30. 

Smart went through the growing pains any rookie point guard on a mediocre team is bound to experience. He scored just 0.59 points per possession as the pick-and-roll ball-handler, coughing the ball up on 23.1 percent of such plays, as noted by NBA.com. He improved substantially as the year progressed, both as an offensive threat and a playmaker, but there is an incredible amount of room for growth.

There's no doubt Smart will be a regular feature on NBA All-Defensive teams for years to come. His development offensively will determine whether he'll be a situational ace or a star.

Best Scenario

On paper, the Celtics improved this summer. They added more depth up front, and the team's young core collectively grew under the excellent tutelage of Stevens. Combined with the fact that the East isn't particularly scary, the Celtics should be in the running for another postseason showing.

The trio of Bradley, Smart and Thomas have enough firepower to cause havoc on both ends of the court. The returning players have had sufficient time to learn Stevens' offensive system, and adding a terrific passer like Lee will only help it flow smoother.

Boston ranked just 20th in offensive efficiency last season, according to ESPN's Hollinger stats. The biggest improvement clearly has to come on that end of the court. The Celtics might not have landed a huge difference-maker in free agency, but cracking the top 15 isn't out of the realm of possibility.

If the Celtics can make strides on offense, they'll be solid contenders for playoff berth. However, improving on last season's seed is highly unlikely.

Worst Scenario

While Boston has an intriguing group of players, there are also a lot of question marks. If Smart or Bradley were to get injured, the backcourt rotation would turn ugly fast. Evan Turner would be relied upon for more minutes, while Rozier and Hunter could be thrown into action as well. That's not a great scenario.

The Celtics might be slightly better this season compared to 2014-15, but so is the competition. No team that finished above Boston figures to take a step back, while plenty of playoff contenders that were out of the loop last year will be back in the mix. The Miami Heat and the Indiana Pacers are two teams that will most definitely be moving up.

There is also the uncertainty of the trade market. If things go south early, Ainge could very well look to move some pieces around. There isn't a phone call he wouldn't take, and that unpredictability will keep Boston fans on the edge as the season progresses.

Predictions

It took 38 wins to secure the eighth seed in the East last season. With Miami and Indiana strengthening their rosters, that number should move up a couple of wins. This Boston team, as currently constructed, will hang somewhere in that vicinity.

Achieving a .500 record is more than realistic and should be sufficient to pencil in Boston as the eighth seed in a weak conference. Injuries to key players are always a concern, but having a team consisting almost exclusively of young players somewhat insures against that.

Even if Boston makes the playoffs, it's highly unlikely it has the experience or the talent level to upset any of the top dogs. That makes another first-round exit the most realistic outcome.

• Final Record: 42-40
• Division Standing: Second
• Playoff Berth: Yes
• Playoff Finish: First-round exit