What is the most challenging element Alabama will face while trying to achieve another repeat in 2016?

It’s not complacency. The ’15 team smashed through that wall.

It’s not a new quarterback. It’s the third consecutive year the team has faced that hurdle, but Lane Kiffin remains the offensive coordinator and Blake Barnett is in the incubator.

RELATED: A look inside Alabama’s QB race in 2016

It’s not losing A’Shawn Robinson, Jarran Reed and Reggie Ragland in the front seven. Jonathan Allen, Tim Williams and Reuben Foster all decided to play one more year.

It’s not replacing Heisman Trophy winner Derrick Henry. That won’t be easy, but the Tide have Bo Scarbrough, Damien Harris and B.J. Emmons.

The biggest potential weakness on the 2016 Alabama Crimson Tide? The offensive line.

The two constants to Nick Saban’s first three national titles at Alabama were a road-grading offensive line and a lock-down secondary. The latter returned in 2015 and should only get better even without Cyrus Jones, thanks to a bevy of five-star underclassmen.

The offensive line, though, must replace two of its best three players from a unit that Henry and Jake Coker propped up in part.

Center Ryan Kelly, first-team All-SEC according to the Associated Press, and right tackle Dominick Jackson, the best run-blocking tackle in the SEC in 2015 according to Pro Football Focus, both are headed to the NFL.

The Tide offensive line was good during the latest championship season. Henry managed to rush for an Alabama single-season record. But many of those yards were created by Kelly and Jackson or even by Henry himself.

According to more advanced metrics, Bama’s line was very good at run-blocking, but far from the best in the country. Teams like Notre Dame, Ohio State, Texas A&M and Arkansas finished with better overall numbers in the running game, according to footballoutsiders.com.

And despite the presence of AP first-team All-SEC left tackle Cam Robinson, who enters his third consecutive season as an Alabama starter, the Tide offensive line fared even worse at pass-blocking, finishing with an adjusted rate of 34th in the country.

Bama allowed a sack on 7.9 percent of passing plays. Looking at more traditional numbers, it was the most sacks that the line has allowed per game since 2010. Anecdotally, Clemson defensive ends Shaq Lawson (with a sprained knee) and Kevin Dodd combined to sack Coker five times in the national title game.

Replacing Kelly will be imperative. The Tide have groomed junior-to-be J.C. Hassenauer in that role, who has yet to start a game. He’ll be facing a wave of former four- and five-star defensive tackles during the SEC schedule with the ever-important task of identifying the line’s blocking assignments pre-snap.

Any mistakes or leaks in pass protection could be compounded. If Barnett does start as a redshirt freshman, it’s imperative that Alabama protects him. He arrived in Tuscaloosa at 6-foot-5 and a frail 190 pounds. He could reach 215 or even 220 pounds by the fall. Barnett’s athleticism comes with good reviews.

But could he lower his shoulder into a defender like the 6-foot-5, 235-pound Coker did on this play?

That’s not to say that this team’s offensive line is going to be bad, or even average. The standard in Tuscaloosa, for better or worse, is championship-level excellence. And that’s not easy to achieve. But there are reasons to at least wonder if the Tide line will reach that tier of performance in 2016.

Alabama, like always, is loaded with options and talent at all five positions.

Junior college transfer Charles Baldwin also is the most likely candidate to replace Jackson at right tackle. Ross Pierschabacher should start once again at left guard as a redshirt sophomore. Alphonse “Shank” Taylor needs to fend off Bradley Bozeman at right guard. Dallas Warmack and Lester Cotton are good enough to push for playing time as well.

Mario Cristobal is your run-of-the-mill position coach underneath Saban — a former FBS head coach who also is an ace recruiter with a deep, impressive pedigree.

In all likelihood, Alabama will feature one of the better offensive lines in the SEC in 2016. It could even be great. The ingredients are there, but the cake hasn’t been baked yet.

In other words, the Tide offensive line will feature a lot of unproven youth next fall. And instead of two returning stars (Robinson and Kelly), it’ll be just one (Robinson).

If Alabama’s offense again is going to lead the team to an SEC championship and a spot in the College Football Playoff, it will be because the team successfully developed several young offensive linemen.

It’ll be a while yet before the team reconvenes for spring ball. But when it does, you can bet that Saban and the coaches quietly will hold a close watch on this year’s Tide blockers.