Could Amir Johnson's feet still be a concern?

His presence is so quietly impactful that his absence doesn't stick out like a hole in your television screen. But it should.

Between the 2014-15 Celtics, who were impressively able to scrap and claw their way to a No. 7 seed in the east, and this year's squad that has solidified itself as a top-tier competitor in its conference there is just one difference on the roster outside the draft selections: Amir Johnson.

That is certainly an oversimplification of the difference between the two teams. This year's group has experienced dramatically lower roster turnover, better and more established rotations, as well as the rise of players who were already here to new levels of effectiveness. But Johnson's game has brought crucial new elements: shot-blocking, a powerful interior presence, and an effective pick-and-roll ability. He is a veteran who has been around the block for 11 years now, and his skill and experience are apparent.

Johnson is as close to a stable, traditional center as the team has come since Danny Ainge made the difficult-to-swallow decision to send Kendrick Perkins packing. Johnson hasn't been the difference-maker in the team's enormous turnaround, but he has been an important piece to the puzzle that relies on everyone playing their role to the fullest potential.

However there have been some concerns when it comes to his ability to stay on the court. Or perhaps it's how the team is managing his minutes that makes you look back on a past decision and wonder.

Before I dig into the statistics behind it, I want to explain the eye test I've conducted on him over the past month or so. If I'm not blind, what I've seen is a player who comes firing out of the gates in games. Whether it's rolling hard to the basket off of picks, getting ahead of the defense for easy transition buckets, or battling for difficult rebounds, he seems to be right in the middle of everything Johnson finds himself heavily involved. That's for about four or five minutes in the first quarter; then he hits the bench and everything changes.

As the game goes on Johnson seems more removed, passive even into the second quarter. As Brad Stevens spins rotations faster than tires on a car through the team's games, more often than not, Johnson finds himself out of the mix.

The numbers are there to back it up too. Johnson is averaging 22 minutes a night, his lowest mark since he was last a full-time bench player in Toronto in 2010. Over the last eleven games since Boston has returned from the break, he has failed to hit the 20-minute mark in nine of them.

Now that would all be fine and well under certain circumstances. The Cs came into the season absolutely jam-packed in the front court. It didn't take long for Johnson to establish himself as a starter, but as he has seemed to fade away in games in the 2016 portion of the season, I can't help but look back on that foot injury that hit him hard in late December.

We've seen it for years in the NBA: foot injuries with big men are scarier than cigarettes to a dry field of grass. Even though he took time off when his plantar fasciitis developed back in December, it wouldn't be out of the realm of possibility to think that it could still be nagging him. It could even be the sole reason for his inconsistent playing time through games.

Dr. Simon Lee commented on the persistence of the infamous condition in NBA players in a Lower Extremity Review article:

"The main difference is that the average person, we would tell them to stop activities that can aggravate their issues until we get them under control, while in a professional athlete we try to have them continue to perform and participate even though their symptoms are not completely gone...so, typically for a lot of NBA players, their symptoms do not completely go away until the season ends and they get a chance to give the plantar fascia a break."

This problem struck Johnson just before Christmas, when Stevens sat him down in a boot for two games. But since then he has played in 36 of Boston's last 37 games, averaging just 6.7 points and 6.2 rebounds per game in about 20 minutes.

Was the problem solved when Johnson sat for just two games? From what Stevens said back then it appeared as though he took valuable advice from people within the organization, but can't be too sure himself what the impact was:

He's been getting it treated, and he's had it for awhile. But I never know to what extent it affects each of these guys. But certainly that's something that you just have to keep a good pulse on and treat well. A lot of these guys have little nagging things like that."

So that leaves us with two conflicting notions. A doctor saying that it's hard to eliminate symptoms of plantar faciitis as the season progresses, but the Celtics decided to give Johnson a two-game break back in December. Ever since then, it has been anybody's guess what kind of time he'll play for a given night.

Whether it is Stevens micromanaging Johnson's condition or not, the inconsistent presence of Amir on the court for the Cs has been damaging because he really does contribute a great deal of production when he is out there going full force. Diving into analytics, he is third on the team in Value Over Replacement Player, first in Defensive Box Plus-Minus, fourth in defensive win shares, and first in regular old blocks.

But through key runs in the game he finds himself off the court whether for strategic or physical reasons. Since the all-star break he has averaged 8.2 minutes per game in the 1st quarter, 4.2 in the 2nd, 5.8 in the 3rd, and a team-low 2.1 in the 4th. Nobody has played less in the fourth quarter since February 19 than Johnson.

In crunch time, for some reason or another, he has not been able to help the Cs. I would say it is reasonable to point to the foot.

Welcome back to the fourth quarter, Amir Johnson. He hasn't played in the fourth since Feb 29 vs. Utah & in only four fourths since Feb. 1.

— Kevin O'Connor (@KevinOConnorNBA) March 16, 2016

As the doctor said it is so hard to handle foot ailments in the NBA. There are too many games and not enough time off to be able to give the adequate rest needed to completely relieve a player of fasciitis. But it makes you wonder: when the Cs were fixated on it back in December, why didn't they give him more time than two nights to get himself right?

It seems as though the Celtics are dealing with a player who they must oversee constantly to ensure he can play for them at all. With strong minutes early in the first and third, it would seem reasonable to assume his minute allocation is health-related.

So with just over ten games left and Boston in the thick of the playoff race it may be too late to shelve Johnson in hopes of having him right for the postseason. As we've seen through their management of him we may not get the full impact of Johnson at all on the team, and it's a shame.

Especially considering the rise of Jordan Mickey in short spurts, looking back on December you have to wonder where Johnson would be now if the team had given him extra time off. It's clear when he is performing the Celts are a substantially better team, but here in March he can't even reach the fourth quarter.

Those big men feet are killers, and Johnson's have quietly undermined this Cs team since December. Their success as a team has overshadowed it, but they could pay the price in a playoff series this spring if he can't play key minutes.