MINNEAPOLIS — Celtics captain Paul Pierce sat out Monday night’s 110-100 loss to the Timberwolves at the Target Center because of “personal reasons,” the team announced.

Pierce did not make the trip; he returned to Boston after the Celtics played Sunday night in New York.

Coach Doc Rivers wouldn’t elaborate on why Pierce missed the game except to say that it wasn’t for any negative reasons, such as an injury.

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Rivers said Pierce “for sure” would play Wednesday night against the Pistons.

Pierce turned his ankle against the Knicks and Rivers said afterward that he was considering resting Pierce, who is averaging 18.8 points, 6.5 rebounds, and 4.8 assists this season.

It marked the second game of the season that Pierce has missed. He also sat out a 100-74 blowout loss in Charlotte last month, though that was to get rest.

Courtney Lee started in place of Pierce, joining a lineup that included Brandon Bass, Avery Bradley, Jeff Green, and Chris Wilcox.

Rivers was asked if he could remember the last time the Celtics didn’t have either Kevin Garnett, Rajon Rondo, and Pierce on the floor at the game time. (Garnett is out with a sore left ankle and Rondo is out with a season-ending knee injury.)

“Oh, vividly,” Rivers said with a laugh.

“About five years ago. It has been a while.”

Confidence growing

Green’s resurgence coincided with the point at which Rondo suffered his injury, but Rivers said he isn’t sure if that’s a coincidence or not.

“Because with the whole heart thing and sitting out a year, you don’t know if this is progression from sitting out a year or if this is just him getting better as a player and getting more confident,” Rivers said.

From the start of the season to Jan. 25, the day Rondo was injured, Green, who sat out last season after undergoing open-heart surgery, was averaging 9.6 points.

Since then, Green was averaging 16.3 points per game entering Monday night, when he scored 10.

“I mean, what did you expect when I first came back?” Green said Sunday night after scoring 27 points in a loss in New York. “I mean, I had to get a rhythm. I was out for a year. I wasn’t going to come back knocking down every shot, penetrating, and doing what I do now. I mean, it was going to take time, and I knew that.”

Rivers said he is enjoying seeing Green’s confidence grow and he pointed to Sunday night’s game as an example.

“You watched the film and he didn’t play very well, but he was very aggressive, and I like the fact that he kept being aggressive, even if the ball kept not going in,” Rivers said. “I thought that was very good. That is a positive step for him.”

Green made 10 of 14 shots against the Knicks.

A spin on rotation

Because the Celtics have been so undermanned the last few weeks, Rivers said he has not been able to set the playoff rotation, unlike most playoff-bound teams at this point.

Rivers said that rotation is at seven players but will increase. The only positive of having so many injured players, he said, was that the Celtics would get a better look at others who might fill out one or two of those playoff rotation spots.

“I just want to see them play,” Rivers said. “We know who we like, but they’ve got to do it every night.”

Said Jason Terry, “Doc made that evident and it was clear in the speech before the game, ‘I want to see who plays in the playoffs. I’ve got to know who I can count on.’ ”

Final thoughts

Garnett traveled with the team to Minneapolis, where he played after being drafted as a 19-year-old until he joined the Celtics in 2007, but he did not play, missing his sixth straight game.

Would the 36-year-old Garnett ever play here again? Rivers said he couldn’t be sure.

“Every year, we don’t know if this is his last time,” Rivers said. “Obviously, I hope not and we all hope not, but you never know with Kevin. Every summer from this point in his career, he’s going to decide whether he’s coming back.

“I would hope that this isn’t [his last year] because you would want him to play his last game here. Let’s hope this isn’t.”

Dooling to Grizzlies

Former Celtics guard Keyon Dooling, who retired from the team last summer and then came back to serve as the team’s director of player development, announced that he has signed with the Grizzlies.

“I want to thank Danny Ainge, Doc Rivers and the entire Celtics nation. Once a Celtic always a Celtic,” Dooling tweeted.

Dooling, 32, has played in 12 NBA seasons and was with the Celtics for 46 games during the 2011-12 season, averaging 4 points in 14.4 minutes per game.

The Celtics had signed Dooling to a one-year deal before he decided to retire after revealing that he had been molested as a child. After the Celtics waived him following his retirement, Dooling became ineligible to return to the club as a player for a year. Dooling had been interested in joining the Celtics to help fill in once Rondo suffered his knee injury, but once it became clear that he couldn’t join them, other teams began to show interest.

The Grizzlies had been looking for a backup to point guard Mike Conley and Dooling served in a similar role as a reserve for the Celtics.