End of the Jared Sullinger era in Boston?

LAS VEGAS -- The Boston Celtics, a team that ranked near the basement of the league in defensive-rebound percentage last season, appear to be letting their best defensive rebounder walk away this summer.

In order to clear enough room to sign free agent big man Al Horford to a four-year, $113 million max contract last week, the Celtics rescinded their $4.4 million qualifying offer to Jared Sullinger, making him an unrestricted free agent.

Sullinger seemed to hint that his days in Boston were numbered earlier in the week when he Tweeted on Wednesday:

Sullinger, the No. 21 pick in the 2012 draft after concerns about his back forced him to slide out of the lottery, put together four quality seasons in Boston. He has averaged 11.1 points and 7.7 rebounds in 24.9 minutes per game for his career. Sullinger played only 23.6 minutes per game last season as the Celtics had both an overstocked frontcourt and a desire to lean on small ball.

All of that plays into why the Celtics might have been hesitant to commit long-term money to Sullinger, a player who has also been dogged by questions about his body shape and conditioning. The Celtics tried stretching out his range to the 3-point line a couple of years back, but cut down those attempts this past season and kept him closer to the basket.

Sullinger was far and away Boston's best rebounder last season, grabbing 27.1 percent of available defensive rebounds, a number that ranked him among the best in the league on the defensive glass. He has steadily improved as an outlet passer. What's concerning for Boston is that the next-best defensive rebounding numbers on the team for a regular came from Jonas Jerebko (19.9 percent) and Amir Johnson (19.4). The team doesn't have an obvious rebounding presence. In Atlanta, Horford grabbed only 18 percent of available defensive rebounds.

There is a small chance the Celtics could climb over the salary cap this summer then offer Sullinger a chunk of the midlevel exception (something that would pay him only slightly more than his qualifying offer at best). Boston could also clear enough cap room to offer him a higher, short-term salary. But it seems more likely that Sullinger will find interest elsewhere in the free-agent market, even if most teams have splurged on early moves.

Sullinger knew his future was uncertain at the end of the 2015-16 season.

"You don't know what's gonna happen, so I really can’t speak upon the future, but if I leave, it's going to be tough walking away from the great guys we have in this locker room," Sullinger said after Boston's season ended in May.

Asked if he expected to be back, Sullinger said only, "I'm not speaking about my future right now."

Sullinger did admit that he needs more consistency in his performance, something the Celtics have stressed to him in recent seasons.

"I've got to do a lot of things better, but it was OK," Sullinger said of his 2015-16 season. "My window is getting smaller and smaller of constantly talking about I need to improve, I need to improve."

The Celtics drafted a pair of international big men -- France's Guerschon Yabusele and Croatia's Ante Zizic -- with first-round picks. But they could be stashed overseas to develop (though Yabusele showed encouraging glimpses Tuesday in summer league after an underwhelming debut Monday). The team is hopeful that second-year big man Jordan Mickey can make the jump to a rotation role, though he's currently sidelined by a shoulder injury at the start of summer league.

Boston has another restricted free agent, Tyler Zeller, who also seems unlikely to return if he gets a big offer sheet, but Sullinger's departure could open the door for Zeller to stick around on a short-term pact.

The Celtics remain hellbent on adding more star power to a core headlined by Isaiah Thomas, Jae Crowder, Avery Bradley, Marcus Smart, Kelly Olynyk and offseason-addition Horford. But Celtics president of basketball operations Danny Ainge has pledged to maintain the sort of flexibility that might help Boston make a bigger splash down the road.