Former Raptors wing Justin Champagnie officially signs on to complete Celtics’ roster

© Winslow Townson Justin Champagnie (left) reaches for a steal in one of his three appearances against the Celtics as a rookie last season.

The Celtics on Friday officially filled their final roster spot by signing Justin Champagnie. The wing was active to face the Raptors, his former team, at TD Garden.

Champagnie signed with Toronto as an undrafted free agent prior to last season and played 36 games as a rookie. After appearing in three more games this season, he was waived in December and had most recently been playing for the G League’s Sioux Falls Skyforce, averaging 18.2 points and 8 rebounds over 23 games.

The University of Pittsburgh product said he had a pre-draft workout with the Celtics in 2021.

“[Celtics president of basketball operations Brad Stevens] said he was monitoring me since I was in college, so that’s always good to hear, just knowing that I was in his thoughts,” Champagnie said. “It was good to hear.”

The Celtics have had an open roster spot since trading Noah Vonleh to the Spurs in early January. Since Champagnie was waived by the Raptors prior to March 1, he will be eligible to join Boston’s playoff roster.

“Being back at this level is amazing,” Champagnie said. “I mean, I spent three months in South Dakota in the middle of nowhere. I’m grateful for it though; don’t get me wrong. I’m grateful for my time over there. But just getting back here and just really trying to hone in and put the work in to make sure that I stick this time.”

Coach Joe Mazzulla said the Celtics are looking forward to getting a closer look at the 21-year-old prospect.

“Anybody that we can add, obviously, he can be a piece for us,” Mazzulla said. “Just intend to make him a part of our player development right now and get him playing a role and kind of see where he is and see what happens.”

Champagnie’s twin brother, Julian, is also in the NBA as a forward with the Spurs.

Brown, Smart, and Brogdon out

Celtics forward Jaylen Brown missed the game against the Raptors due to a laceration on his right hand. He said he cut the hand on a vase while watering plants, and that the wound required five stitches.

Brown said he expects to be sidelined for up to a week, and will be able to return in time for the start of Boston’s first-round playoff series next weekend.

Guard Marcus Smart, meanwhile, missed a second game due to a pinched nerve in his neck.

“He got treatment [Friday],” Mazzulla said. “It looked like his neck was still hurting a little bit. But I don’t expect it to linger into the playoffs or anything.”

Guard Malcolm Brogdon sat out with what was listed officially as lower-back pain. It was essentially a rest day for the Sixth Man of the Year candidate, with Boston locked into the No. 2 seed in the Eastern Conference playoff bracket.

Mazzulla mourns former coach

Former West Virginia assistant coach Billy Hahn, who worked closely with Mazzulla during his time as a point guard with the Mountaineers from 2006-11, died Friday at the age of 69.

“He was just a guy that brought a level of energy and mind-set the entire time, no matter what was going on,” Mazzulla said. “He was a player’s coach. He was there for me whenever I needed him, on and off the court, and he just had a loyalty and a work ethic about him, and a personality that you just wanted to be around him. So it’s definitely somebody we’re going to miss, but definitely somebody that I’m grateful that I’ve had in my life that has helped me get to where I am.”