By Brian Robb, CBS Boston

BOSTON (CBS) – The Celtics’ 2015-16 season is just getting started, but for Jared Sullinger, the work has lasted all summer long.

The fourth-year power forward is at a crossroads in his career as training camp kicks off. His injury and conditioning issues limited him last season, leading to Danny Ainge calling him out publicly back in January for a lack of progress on that front. Months later, Sullinger is entering a contract year in a crowded frontcourt, where his playing time and development is no longer guaranteed.

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In order to combat that situation, Sullinger has spent the entire offseason working out with former NBA star John Lucas in Houston, as he attempted to get his weight, and conditioning under control for the upcoming season. The 23-year-old reflected on the situation at Celtics media day on Friday, noting how his family staged an intervention to try to bring the conditioning issues to his attention.

“It’s my mom, my dad, my brother Julian, David Falk, Danielle Cantor and this bald-headed guy by the name of John Lucas,” Sullinger said of the meeting this summer. “And [Lucas] personally came down and told me. He said I have all the talent in the world, but you forgot what working hard is.  And you know, for somebody to come from Houston all the way to Columbus, Ohio, to stop whatever he was doing, meant he was there for me. That’s what made me go workout with John.”

Lucas battled his own demons in his career, facing multiple suspensions from the league for drugs. He’s worked in recent seasons with troubled NBA and college players to help them learn from their mistakes. Even though Sullinger has a different set of issues than substance abuse, the lessons from Lucas held strong.

“I think John’s biggest focus was to not let me make a mistake,” Sullinger explained. “Sometimes it’s not always drugs, it could be other things. And he wanted to just clear my mind and understand that I can be whoever I want to be, I’ve just got to make the right choices. And being there with John really helped me out.”

The work Sullinger put in was all over the sports spectrum with Lucas, but all of it proved to be valuable according to the big man.

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“I mean I went from boxing to swimming to on the court basketball to on the track. I did so many other sports other than basketball. There was one point where I was down there in August for two weeks and I didn’t touch a basketball. He wouldn’t let me. We just got in shape other ways. It was a lot of fun,” Sullinger said.

As the beginning of training camp unfolds, the former Ohio State star isn’t sure he’s at where he wants to be with his body. He won’t know that until the real games begin. For the time being though, his focus will be able to stay on his play, instead of whether he can actually stay out on the floor at all for extended stretches.

“There’s a difference between being in the best shape you can be, practice-wise, and then there’s game shape,” he said. “So we’ll see when that happens. But as far as me being where I want to be, I’m not there yet, but I’m closer than you will imagine.”

As for his playing time and a new potential contract, Sullinger is adamant that his priorities remain elsewhere, as he shoots for a return trip to the postseason.

“I never set personal goals for myself,” Sullinger said. “Everything is between the team, everything is team oriented. My biggest thing is just win as many basketball games as we can and build on what we had last year and understand we can be whoever we want to be as long as we put our mind to it and as long as we understand that we can’t be selfish.”

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Brian Robb covers the Celtics for CBS Boston and contributes to NBA.com, among other media outlets. You can follow him on Twitter @CelticsHub.