By Brian Robb, CBS Boston

BOSTON (CBS) — Out of all the potential stars that might be available at the trade deadline for the Celtics this week, none of them have a better contract than the Bulls’ Jimmy Butler.

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The 6-foot-7 wing is under contract through the 2018-19 season for an average of just $19.2 million per year, making the 27-year-old swingman a bargain for his production (24.5 points, 6.3 rebounds, 5.0 assists per game).

Putting up those type of numbers on a discount deal gives the Bulls front office plenty of reason to ask for a massive return for the three-time All-Star, if they elect to move him at the trade deadline this week. According to a new report from TNT’s David Aldridge, that’s exactly what they are doing in negotiations this week. There’s no question that the Celtics would need to deliver a strong collection of young players (Jaylen Brown) and draft picks (one of the Brooklyn selections at least) to get serious in negotiations. However, it’s the additional sweetener to that core package that is making Danny Ainge wary, according to Aldridge.

“I think the Jimmy Butler stuff is real,” Aldridge told NBATV’s GameTime on Tuesday night. “[The Celtics] have been trying to get Jimmy Butler. [Ainge] doesn’t want to give up Jae Crowder. That’s the main sticking point there and he doesn’t want to give up Jae Crowder in a deal and that’s the guy the Bulls are insisting on right now in any package for Butler.”

Ainge’s insistence on keeping Crowder makes a lot of sense when you look at the big picture of what Ainge is trying to do. Crowder is one of the best bargain contracts in the NBA right now, earning an average of $7 million per season through 2019-20. He’s also in his prime at age 26 and in the midst of a career year, shooting over 40 percent from 3-point range and averaging over 14 points per game.

Replacing that type of production as well as Crowder’s defensive versatility on the wing is impossible to do at that price. The cost certainty within Crowder’s contract also makes him an extremely valuable tool for team-building purposes, allowing Ainge to bring more assets on board in future years without going over budget.

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Butler is a nice piece for Boston, but you need a strong supporting cast to take down the likes of the Cavaliers, and that’s a reality that Ainge appears to be set on maintaining.

“The picks will work themselves out,” Aldridge said of the negotiations with Chicago. “Boston has about 600 first-round picks in the next five years, so they’ll make it work. That part I’m not worried about. I think it really comes down to Crowder. In terms of real tangible players I think Danny would like to go into the playoffs with Smart, Bradley, Crowder defensively along with Butler, Horford, Thomas offensively. I think he feels like that’s the only way they’ll be able to compete with a team like Cleveland.”

While Ainge may elect to draw a line in the sand on adding a vital piece like Crowder to the package, the Bulls understandably want to hold out for a more convincing return. There’s uncertainty surrounding any Brooklyn pick or a young prospect like Brown. At least with Crowder, they know they would be getting a proven player, even if he’s not a star.

“Chicago, I think rightly, is saying, ‘If you want our best player, we’re not going to just do it for picks,” Aldridge explained. “‘We’re not going to take guys you aren’t going to keep on your roster. We want a guy that is going to be able to grow with us, along with one of those high picks.’ They want a top half of the lottery type of pick for Jimmy Butler, along with a starting established player under contract. I understand that from Chicago’s point of view.”

With mere hours until the deadline, it’s not clear just yet whether either side should or will blink in negotiations. This is a deal that could certainly be revisited after the season so there’s no true sense of urgency for either side right now.

The Celtics surely want to make a run at a potentially vulnerable Cleveland team this year, but adding Butler and giving up Crowder might be a situation where it’s two steps forward and one step back for Boston in that quest.

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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