For months, all Jared Sullinger had was time.
He lay in bed on doctor’s orders, his 6-foot-9-inch, 260-pound frame largely immobile, playing video games, watching movies and basketball clips of himself as one day melted into the next, as he waited for his back to heal.
Then about two weeks ago, the Celtics forward, whose rookie season was cut short by lumbar disk surgery, was cleared to start working out again. He called his father, Satch, in Columbus, Ohio, who heard in his son’s voice both relief and enthusiasm.
Sullinger was excited, Satch said, just to be able to work up a sweat again.
The process of rehabbing isn’t to be rushed. Tedious steps must be taken delicately, as if to remind the body’s owner of its fragility.
This was all new to Sullinger, who had never had such an operation. Trudging through the painfully slow process of rehab, he said, forced him to “find himself.”
Sullinger is now upright, in the midst of, he said, a 10-week plan: Every two weeks, the intensity of his workouts increases by about 10 percent.
And by September or October, when training camp begins, he hopes to be close to 100 percent.
“I’ve got 10 weeks to get back to where I was or even better,” he said Thursday at a “Stay in School” assembly at Northeastern University’s Matthews Arena, where the Celtics honored 1,500 middle school students from Boston public schools.
A cloud of uncertainty hangs over the Celtics, with questions about whether Paul Pierce and Kevin Garnett will wear green next season. And there’s similar wonder about whether Sullinger, who averaged 6 points and 5.9 rebounds over 19.8 minutes last season, can be himself again.
It’s a legitimate question considering he’ll be less than a year removed from surgery to repair a back that has been problematic since his career at Ohio State, an issue that caused him to fall to the 21st overall pick in the 2012 draft.
“Everybody says ‘back’ with a question mark, [but] you might as well put an X through that,” Sullinger said. “Because I had surgery, I’m taking my time and getting back right. [There] won’t be no recurring injuries.”
Those close to Sullinger don’t doubt he’ll return as good as new — perhaps better.
Former Boston College and Ohio State standout and European pro Scoonie Penn, who has known Sullinger for years and was with him on draft night when the Celtics called, believes it because of Sullinger’s will.
“He loves the game,” Penn said. “He loves getting better. And he’s going to do whatever it is, within his power, to get better, to become that player, because it’s important to him.”
Jeff Boals, an assistant at Ohio State, believes it because of Sullinger’s even-keel attitude.
Boals recalled only a two-week stretch in Columbus in which Sullinger seemed anything but levelheaded. It came when opponents were battering him down low, trying to take him out of his game, and officials stood idly by, their whistles silent.
“That was the only time in his two years when he showed any type of negative mentality,” Boals said. “He was always just a positive guy. He always had a great attitude. And I think that’s really helped him in this situation.”
Of course, Sullinger’s father has shared advice, telling his son that this is all a life lesson.
“And I think for a 21-year-old, the lesson is patience, because you’ve already heard that you’re going to come back 100 percent,” Satch said.
“So it’s not worrying about whether he’ll be back or not. It’s just being patient. And following directions of the medical staff and the trainers to get you back.”
“I’m getting a test of my patience, my discipline — because I had to be really disciplined while I had back surgery,” he said. “This is a test, and I’m just learning the lesson now.”
One day, Satch said his son will be able to use this lesson when he’s married, and when he has children of his own.
“He’ll be able to draw from these experiences,” Satch said.
Rehab can be lonely — just you, your recovering body, and time — but Sullinger kept close to his teammates, going to games and practices. He dressed in warm-up gear before games and took shots here and there.
He has also kept in close contact with Rajon Rondo, who underwent season-ending knee surgery in February.
“I have someone I can lean on,” Sullinger said. “Somebody that can support me through my injury.”
Being sidelined also helped him view the game from a different angle.
He now understands more about his game, about the NBA game, about the Celtics and what they need to improve on going forward.
Sullinger said he won’t play with the Celtics’ summer league team in Orlando, calling it a “smart move” as he recovers.
After all, he doesn’t want to prematurely rush back to action.
He is, however, confident that the way he was playing before he had surgery, when he was averaging 7 points and 7.2 rebounds (2.5 of them offensive) in January, is a foundation upon which he can build.
“Honestly, when I was playing, I was playing on one leg,” he said. “My right leg was pretty much dead. I couldn’t push off. Didn’t have no strength behind it.
“With the right leg being the way it was, and still being able to produce the way I did, I guess it sets a bit of a foundation, but mentally I know I can play better.”
Sullinger said fitness isn’t great, but he’s working on it.
“I got a lot of process to go,” he said. “By the time I need to be where I’m supposed to be, I’ll be great.”
That is the goal he is working toward. All that stands between him and reaching it is time.
. . .
Beginning on Friday, the Celtics will host up to 12 draft prospects for workouts over two days, NBA sources said. Six are point guards, a position where the Celtics could use some help: Shane Larkin of Miami, Phil Pressey of Missouri, Pierre Jackson of Baylor, Peyton Siva of Louisville, Erick Green of Virginia Tech, and Myck Kabongo of Texas. Centers Jeff Withey of Kansas, Steven Adams of Pittsburgh, Colton Iverson of Colorado State, and Greg Echenique of Creighton are also scheduled to attend. The Celtics have the No. 16 pick in the first round on June 27. They do not have a second-round selection . . . The schedule was announced for the Orlando Summer League. The Celtics will play July 7 against Orlando, July 8 against Detroit, July 9 against Indiana, and July 10 against Houston. Games on July 12 are TBD . . . Sullinger said he hasn’t talked to Garnett or Pierce and that he doesn’t know whether they’ll play for the Celtics next season, but he said he supports them either way.