Sam Cassell, an assistant coach with the 76ers this season, will reportedly join Coach Joe Mazzulla’s staff in Boston. David Zalubowski/Associated Press

The Celtics were looking to add an assistant coach with NBA experience to their staff this summer. Just days into the offseason, they found one.

Sam Cassell – who was a member of the Celtics’ championship team in 2008 – will join Boston’s coaching staff as an assistant under Joe Mazzulla, according to a report Sunday from The Athletic.

Cassell, who played 15 years in the NBA as a point guard and was a three-time champion, has been an assistant coach for the last 14 years, including the last nine under Doc Rivers in Los Angeles and Philadelphia. Rivers was fired by the 76ers last month after the Celtics eliminated them in the second round, and Cassell was reportedly in the mix to replace him before Nick Nurse was hired.

Cassell is very highly regarded in basketball coaching circles and it seems likely he’ll be the Celtics’ top assistant under Mazzulla, whose coaching staff is being replenished after he worked shorthanded in his first season as a head coach.

The Celtics lost top assistant Damon Stoudamire in March, and he was never replaced despite attempts in doing so. On Friday, Ime Udoka revealed he intends to hire away multiple Celtics assistants – who had initially followed him to Boston in 2021 – to work under him with the Rockets. Ben Sullivan, who was Boston’s top assistant after Stoudamire departed, Mike Moser and Garrett Jackson are reportedly leaving to join Udoka’s staff in Houston, and Celtics assistant Aaron Miles is also reportedly drawing interest for a new job.

Celtics President of Basketball Operations Brad Stevens said Thursday at his end-of-season press conference that the team was going to add at least one assistant with NBA experience and the 53-year-old Cassell fits the bill. Paul Pierce, who was a teammate of Cassell on the 2008 title team, endorsed him during a Showtime podcast last week.

“These cats went to the Finals,” Pierce said in a recent episode of the “Truth and Ticket” podcast. “They were one game away from the Finals. You’ve just got to take a deep breath and say, ‘Where do we get better at?’ It starts at the top. …

“You can’t keep bringing in new voices. I’m going to add to what I got right now. I’ve got to add to it. It’s already good. I’ve got to add to it. It’s already there. So, I’m bringing Mazzulla back but maybe I’m bringing in a veteran coach, like Sam Cassell. Some influence on the bench. Respect. A champion. Been a coach. Understands what it takes.”

THE CLIPPERS are promoting Trent Redden to general manager while keeping the core of their front office together by promoting Mark Hughes to senior vice president/assistant general manager.

By selecting Redden as the team’s second-highest-ranking basketball executive, President of Basketball Operations Lawrence Frank chose someone he has worked with since 2017 when Frank hired Redden as the Clippers’ assistant general manager while building a brand-new front office.

Redden has overseen much of the team’s scouting operations while also overseeing its G League affiliate in Ontario. He fills the general manager position left vacant last week when Michael Winger was hired as Washington’s president of Monumental Basketball.

SUMMER LEAGUE: Victor Wembanyama’s next couple of weeks are now set: He’ll be playing in the French league finals starting this weekend, and then the San Antonio Spurs will almost certainly make him the No. 1 pick in the NBA draft on June 22.

And if that means the French star’s summer league debut comes in Sacramento instead of Las Vegas in early July, the league is fine with that.

NBA Commissioner Adam Silver said the league doesn’t have a preference regarding the site of Wembanyama’s first game with the Spurs. While the NBA Summer League in Las Vegas is the biggest – all 30 teams attend – and commands the most attention, there are smaller summer leagues that precede the Vegas event by a few days. Sacramento plays host to one of those events, and the Spurs are one of six teams headed there this year.

“All summer leagues are NBA Summer Leagues,” Silver told The Associated Press. “I’m very supportive of the Sacramento summer league. I remember when (Kings owner Vivek Ranadive) first came to the league and said this was something he wanted to do. I said, ‘As long as you have enough other teams who support it and players who want to play in it, it’s a good thing.’”

The Kings might be getting a lot more buzz than usual this summer. Not only are the Spurs headed there, but so is Charlotte — which holds the No. 2 pick. And it just so happens that the Spurs and Hornets will open Sacramento summer play against one another, potentially setting the stage for a No. 1 vs. No. 2 matchup a few days before Vegas even starts.

If Wembanyama plays in Sacramento, he’d be the first No. 1 pick that didn’t debut in Las Vegas since Markelle Fultz for Philadelphia in 2017. The 76ers played in Utah’s summer league that year before going to Vegas.