Despite a collection of assets that are all performing above expectations, Boston Celtics general manager Danny Ainge's philosophy has been clear since even before last summer's NBA draft.

"There’s no such thing as untouchables," Ainge said, per ESPN's Chris Forsberg. "But there’s guys that we really love and are part of our core that we don’t want to move."

Since the Celtics have an abundance of lucrative draft picks on top of some intriguing talent, it's only natural for the team to be connected to any rumblings surrounding superstars. If one suddenly becomes available, anything goes.

Ainge may not believe in the concept of untouchables, but there are several players who he should fight to keep no matter what happens moving forward.

Isaiah Thomas

Is Isaiah Thomas the point guard of the future for the Celtics? It's not unreasonable to ask.

He stands at just 5'9" and will always have trouble defending bigger guys at his position. That's something that can be particularly exposed in the playoffs. As he makes his All-Star debut this year, Thomas' market value is unlikely to ever be higher than it is now, which is theoretically the best time to shop players.

On the flip side, moving Thomas at the trade deadline is practically out of the question. He is the catalyst in head coach Brad Stevens' offense, which falters immensely in his absence. Boston puts up 105.5 points per 100 possessions with Thomas on the court, and the figure drops all the way to 97.7 when he sits, per NBA.com. That's the difference between ranking sixth and 28th in offensive efficiency, per ESPN's Hollinger stats.

Without Thomas, Boston loses most of its creativity. There is no one on the roster who can replicate his maneuvers around the basket, or penetrate the lane with equal conviction and efficiency. He ranks fifth in the league in drives, per NBA.com, and his ability to draw help defenders opens up space for his teammates.

The Celtics are establishing themselves as serious contenders for home-court advantage in the playoffs, and moving Thomas would seriously jeopardize that, regardless of the incoming talent. There simply isn't sufficient time to re-work the offense, which so heavily relies on the starting point guard.

It's a real possibility that Boston will take a step back in the offseason to make some drastic moves, but Thomas is essential in the short-term picture and should stay put past the deadline.

Jae Crowder

If anyone felt queasy when Jae Crowder inked a five-year, $35 million extension with the Celtics last summer, any anxiety should have evaporated by now. 

Crowder is already outperforming his contract, and he won't earn over $8 million in a single season until the end of 2019-20, per Basketball Insiders. That's an absolute steal, especially for a versatile forward who can play multiple positions.

Perhaps Crowder can't carry an offense, but he works exceptionally well as a secondary driver. He is more confident than ever attacking the basket and has bumped up his three-point percentage to a respectable 34.8 over a moderate sample size.

Experts are starting to notice Crowder's contributions, including ESPN's Zach Lowe on his recent podcast:

I think Jae Crowder is the best player on the Celtics right now. It sounds weird to say that because I didn't name him to my All-Star team and I did name Isaiah Thomas, and it's kind of indicative of the weird and complex nature of basketball. Jae Crowder to me is their best overall two-way player.

It may still be a stretch to anoint Crowder Boston's best, seeing as he is more of a glue guy on both ends of the court than a creative force, but his value is undeniable. He has made a tremendous leap, fulfills his role to perfection and provides Stevens with a practical piece to plug in where needed.

Small forward is a shallow position in the NBA, and many teams would love to have someone like Crowder locked up on a cheap deal for years to come. Even though he may be in demand in potential trade talks, it's highly unlikely Crowder is going anywhere anytime soon, unless the return is a monumental superstar.

Marcus Smart

Marcus Smart's short career has been one of extremes. He has met every expectation as a tremendous defender. Few in their early twenties possess an inherent will to hound opponents into despair the way he does. Unfortunately, injuries have equally slowed down his progress on the offensive end.

Smart has already missed 21 games this season, which has demoted him from starter to key bench cog. He has done well in his role, however, and is looking increasingly more confident when exploring his offensive limits, as proven by the triple-double in the 117-103 victory over the Phoenix Suns on Jan. 15.

Stevens certainly likes what he sees in the 21-year-old guard, and he's just as eager as everyone else to see to see where Smart's gritty attitude can take him, per Darren Hartwell of NESN.com:

"I say this out of respect for his game—I don’t think confidence is ever an issue. I think he’s a physical kid, he’s a competitive kid, he believes he belongs out there and he believes he can excel out there. And he’s getting better every time he takes the court."

Smart needs to develop a consistent jumper, improve his ball-handling and become a more aware playmaker, but he can get there. Chicago Bulls' Jimmy Butler started his career on a similar path, and it took him several years to evolve from a three-and-D role player into a legitimate superstar. Even if Smart doesn't have the same upside, there's no reason he couldn't be an All-Star one day.

With Smart being held in such high regard by the Celtics, his internal value to the team should naturally be skewed in contrast to his true worth on the market. That fact alone would make his inclusion in any deal difficult.

All statistics are accurate as of Feb. 8.

You can follow me on Twitter: @VytisLasaitis