By Brian Robb, CBS Boston

By Brian Robb, CBS Boston

BOSTON (CBS) – Danny Ainge has emphasized flexibility in the midst of the Celtics rebuild over the past two seasons and that’s a trend that will continue when it comes to potential contract extensions for Tyler Zeller and Jared Sullinger.

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According to Adam Himmelsbach of the Boston Globe, the Celtics will not come to terms on extending the big men for upcoming seasons once the negotiation deadline passes this evening.

The lack of an agreement should not come as a surprise to Celtics fans. Despite Sullinger’s stellar start to the season, the 23-year-old has not really proven himself as a worthy long-term investment yet for the Boston brass, after the team watched him deal with injury and conditioning issues throughout his first three NBA seasons. Sullinger’s agent David Falk is not known as someone who is willing to take a team-friendly discount while trying to gain his client security either, making the chances of a deal low from the start of negotiations.

Ainge will have no problem paying for Sullinger if he proves his worth with consistent play all year, but that’s an answer he will have no trouble waiting for next July.

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Tyler Zeller #44 of the Boston Celtics (Photo by Maddie Meyer/Getty Images)

Tyler Zeller #44 of the Boston Celtics (Photo by Maddie Meyer/Getty Images)

Zeller’s situation was a more intriguing one. He thrived in Brad Stevens’ pace-and-space system last year, averaging a career-high 10.2 points and 5.7 rebounds in just 21 minutes per game. Despite earning back his starting job in training camp, the seven-footer has labored through his first three games this year, and was even benched after just seven minutes of action on Sunday against the Spurs.

The lackluster stretch is certainly poor timing for the 25-year-old who likely was hoping to earn the stability of a $10 million per year contract for the next couple years in the face of skyrocketing salary cap in the next couple years.

Unproven bench players, including Jeremy Lamb of the Charlotte Hornets was given a $7 million annual salary for the next three years in a deal announced Monday. That agreement gives Zeller plenty of ammo for asking for a extension in the tens of millions, but that’s hard for Boston to commit to, knowing Zeller is a guy who hasn’t seen the floor for more than a few minutes in the second half of three games this year.

The lack of agreements for both players does not necessarily mean either player is any less likely to remain in Boston long-term. Zeller and Sullinger will both be restricted free agents after this season, giving Ainge the right to match any offer they receive in the open market next year. Leaving both guys unsigned now also has its advantages as it leaves each player with small cap holds of $6.5 million and $5.7 million respectively next summer. Those modest numbers will help Ainge better maneuver with his cap room in his attempts to land a high profile free agent or explore blockbuster trade options.

In the meantime, both guys will have to prove their worth in a crowded frontcourt while facing the pressure of a contract year. Not exactly an ideal situation, but both will have ample opportunity to show they can be reliable rotation pieces for the future.

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Brian Robb covers the Celtics for CBS Boston and contributes to, among other media outlets. You can follow him on Twitter @CelticsHub.