Dave Lewin, general manager of the Maine Red Claws and scouting director of their parent Boston Celtics, confirmed Monday what many had suspected for months: Scott Morrison, the most successful coach in Red Claws history, will join the staff of Brad Stevens in Boston as an assistant coach.

Morrison, 39, led the Red Claws to three straight Atlantic Division titles in the NBA Development League and helped develop league Rookies of the Year Tim Frazier and Abdel Nader. Because Morrison’s current contract runs through June 30, no official announcement will be made until July.

“Scott will be joining the Celtics for next season,” Lewin said. “You can go ahead and say that.”

The Celtics currently have five assistant coaches: Jay Larranaga, Micah Shrewsberry, Walter McCarty, Jamie Young and Jerome Allen. The new coach of the Red Claws appears likely to come from that pool.

“It’s not done yet and perhaps something different will happen,” Lewin said, “but my impression is that several people will shuffle internally. Brad will have the lead on that. We’ll take a look at a couple of people who have been with us in Boston and are ready to have the opportunity to be a head coach.”

The Celtics will take part in two weeklong Summer League sessions. The first starts Sunday in Salt Lake City with Allen as head coach, and the second starts July 8 in Las Vegas with McCarty as head coach. Morrison will be on staff for both sessions.

“I think they’re still deciding what my role (with the Celtics) will be,” Morrison said by phone Monday afternoon from Boston. “(Stevens) suggested I’ll most likely be on the second bench. I just want to try to do the best job I can here.”

The first week of July also means the opening of free agency, and “we have some important things going on with that that we’re going to pursue pretty aggressively,” Lewin said. “That will flow right into Summer League and during the tail end of Summer League or right after, the D-League (now known as the G-League) will be the next priority.”

Of the 15 players on Boston’s current roster, James Young, Jonas Jerebko, Amir Johnson and Gerald Green soon will be unrestricted free agents and Kelly Olynyk could be a restricted free agent. Tyler Zeller and Jordan Mickey have nonguaranteed contracts for next season and Demetrius Jackson has a guarantee of $650,000.

“So more than half our roster could potentially change, depending on trades and free agency,” Lewin said.

One thing that should remain stable is the parent club’s reliance on Portland as a place to keep its bottom-of-the-roster players active and game ready.

“Organizationally, we’re all in,” Lewin said. “Everyone has seen the value of what we’re doing in Maine and the importance of it as a preparatory opportunity. For guys who are not quite ready to be Celtics, we want to get them ready to be a part of what we’re doing.”

Of the four players selected by the Celtics in last week’s NBA draft, Kadeem Allen at No. 53 and Jabari Bird at No. 56 are likely to be mainstays of the Red Claws. Semi Ojeleye at No. 37 and, although less likely, even Jayson Tatum at No. 3 also could see considerable G-League action.

“Depending how things go,” Lewin said, “all rookies have a chance to spend some time in Maine.”

Morrison recently became engaged to Susanne Canvin, a fellow Prince Edward Island native who played college basketball in Canada and works in marketing and advertising for the Celtics. They are living in Boston.

“I’m happy to get the (NBA) opportunity, but I was definitely happy to be (in Portland),” Morrison said. “In this business, it’s move up or get out. In a different environment, I’d sign a 10-year contract to stay there (in Maine).”

Glenn Jordan can be contacted at 791-6425 or:

[email protected]

Twitter: GlennJordanPPH