With Tuesday’s season opener against the 76ers fast approaching, the Celtics are in the late stages of finalizing their roster.
In past years, Boston has sometimes kept one spot open for added flexibility. But according to a league source, the team is planning to enter the year at the maximum allotment of 15 players, in large part because of the season-ending ACL tear forward Danilo Gallinari suffered last month.
The source said the Celtics will continue to keep tabs on cuts around the league, but the final spots will most likely be filled by players who are part of Boston’s training-camp squad.
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Forward Noah Vonleh’s extended opportunities during the preseason are no accident, and the source said the former first-round pick is best positioned to secure one of the final two open spots. Vonleh, a Haverhill native, started Boston’s 112-103 win over the Hornets last Friday and had 14 points and 13 rebounds.
“This is a great opportunity,” said Vonleh, who played in China last season. “I got the call in early August from the front office and they talked to my agent and told me there was a potential chance to make the roster. I was very excited, especially being a hometown kid from the area. I just came here with the right mindset trying to take it day-by-day.”
The Celtics recently waived Bruno Caboclo, Denzel Valentine, and Luka Samanic. Valentine and Samanic are set to join the team’s G League affiliate in Maine because they’d agreed to Exhibit 10 deals. They’ll still be free to sign with other teams, but will receive $50,000 if they spend 60 days in Maine.
Also, the source said the team is waiving guard Brodric Thomas, who was on a two-way contract with the Celtics last season. Boston does not hold Thomas’s G League rights, so he was not on an Exhibit 10 contract.
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So veteran forwards Justin Jackson, Jake Layman, and Mfiondu Kabengele are likely vying for the final spot. Jackson, the 15th pick of the 2017 draft, averaged 6.5 points and 2.5 rebounds over six NBA seasons, and was signed to a 10-day contract by the Celtics last season before contracting COVID-19. A league source said the team had discussions then about keeping him for the rest of the year before ultimately signing Nik Stauskas. Jackson had 16 points and 4 rebounds in last week’s win over the Hornets.
Layman, a second-round pick in 2016, averaged 4.8 points and 1.7 rebounds per game over six total seasons with the Trail Blazers and Timberwolves before becoming a free agent at the end of last season. The Norwood native had 5 points in 16 minutes against Charlotte last week.
Kabengele, a first-round pick in 2019, was one of the stars of Boston’s summer-league squad and signed a two-way contract with the team then. But since he is already under contract, the Celtics are unlikely to have urgency to convert it to a regular NBA deal now. Boston is expected to make its final roster decisions soon after Friday’s preseason finale against the Raptors in Montreal.

The Celtics continue to have discussions with fourth-year forward Grant Williams’s camp about a contract extension ahead of Monday’s deadline, but nothing appears imminent. As of Thursday afternoon the two sides were essentially at a stalemate, a league source said, but that’s fairly common at this stage. Williams is believed to be seeking a four-year deal with an average annual salary of around $13 million to $17 million, but the Celtics’ offers have fallen short.
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Regardless, the source stressed Williams will remain an important part of the Celtics’ future whether he signs an extension now or becomes a restricted free agent next summer.
The Celtics also have an opening on the coaching staff after assistant Joe Mazzulla was elevated to head coach in place of Ime Udoka, who has been suspended for one year due to violations of team policies.
In recent weeks the team’s brass checked in with several coaches about joining Mazzulla’s staff, including Clippers assistant Jay Larranaga, a longtime Celtics assistant. But a source said Thursday that the Celtics are confident in their current staff and have decided to move forward without making an addition.
Over the past week the Celtics have been busy fortifying the roster of their G League affiliate, the Maine Celtics. Samanic, Valentine, Roxbury native and former Providence star A.J. Reeves, and center Reggie Kissoonlal will join the squad after signing Exhibit 10 deals. A source said the Celtics are expected to add one more player on an Exhibit 10 contract before the preseason ends.
Adam Himmelsbach can be reached at adam.himmelsbach@globe.com. Follow him @adamhimmelsbach.