It’s only been a week since the Celtics acquired Jeff Green, but the Celtics are already trying to figure out one small problem: What are they going to do with him? Honestly, Doc Rivers doesn’t really know the answer to that yet. He has slotted him in behind Paul Pierce at the small forward spot, but beyond that, the coach is looking for more ways to utilize his new 6-foot-9 player.

This is the problem with being “multi-dimensional,” the trait most often ascribed to Green, as opposed to singularly awesome. Troy Murphy can make 3’s and rebound. Nenad Krstic is a nice offensive player and a big body.

Green is something else and Rivers and his coaching staff have to identify and unlock the dimensions they want to utilize. Is it his ability to create his own shot, something the second unit desperately needs? Should Rivers try to take advantage of his quickness at the four, or his size at the three?

“I haven’t figured out how to use Jeff yet,” Rivers said Thursday after the team ran through practice at Waltham. “I’ve got to figure that out quickly.”

In three games with the Celtics, Green has recorded just 18 points and four rebounds (and zero assists) and has not topped 20 minutes once. That’s quite a comedown for a player who was putting up 15 points in 37 minutes a night with the Thunder, but Green said that he’s not concerned.

“Things might look a little shaky but it’s going to take time,” he said before making his Boston debut Wednesday night. “You can’t come to a team like this where you have heady vets and try to come in and be successful right away. It’s going to take some time.”

Asked specifically about adapting to a new role that wasn’t as defined as the one he had in Oklahoma City, Green said he was all for it. “It’s great. It gives me a chance to expand my game,” he said. “It’s all for one goal. No matter how many minutes I play, no matter what my role, is I’m going to do the best I can to complete that role.”  

But what role is that going to be? It’s still not clear yet.

This is what Celtics president Danny Ainge said during an interview on The Big Show on WEEI:

“Doc’s toughest job is the Jeff Green piece. The most difficult transition is going to be Jeff Green because Jeff is so capable of playing so many different things to maximize his talents. He's got so much to offer, I think that's Doc's single focus, seeing the things he can do and how to best utilize him.”

Rivers and his coaches are breaking down film and holding extra sessions with his new arrivals in an effort to get them up to speed. They’ll have them go through a mini walkthrough Friday morning and then a team session Friday night before they play the Warriors.

After practice Thursday, assistant coach Armond Hill ran through the offense with Green, Krstic, Murphy, Sasha Pavlovic and Chris Johnson. Then Lawrence Frank ran them through the defensive paces, reinforcing team concepts like communication, shrinking the floor and not allowing corner 3’s.

Of all the new additions, Krstic is the easy one. He’s the only healthy center on the roster and his game translates well to a team that looks to make the extra pass.

His back to the basket game has also been something of a revelation. Thunder coach Scott Brooks told Rivers that Krstic was a good post-up player, but on a team with Kevin Durant and Russell Westbrook, he didn’t have much need for those skills.

“I’ve got to say, I’m shocked at how easily he’s fit in,” Rivers said. “I thought it would be Jeff. So far it’s not even close. Nenad just plays off of people. Jeff needs the action.”

What he needs is Delonte West. With West out, the Celtics’ second unit has been forced to improvise. At times they have looked sensational, like in the first half against Phoenix. At others, they’ve looked dreadful – like in the second half of the same game.

Like most people, the Celtics believe that Green was forced to play out of position in Oklahoma City and that his natural position is small forward. There are only so many minutes to be had playing behind Pierce and Rivers has tried a couple of different options with Green, including playing the two of them together.

“Teams are going bigger at guards and when they do that it helps us because now we can put Jeff and Paul on the floor at the same time,” Rivers said. “As long as it’s not the runners. We don’t want Paul or Jeff chasing the Ray Allen’s of the world. It does create a matchup.”

That may be fine in limited doses, but that’s not a natural fit for Green either. The other spot he could help is at the four where the Celtics are fairly well set with Kevin Garnett, Glen Davis and Murphy.

Davis will be out for about a week with a strained patella tendon in his left knee and that should open up some time for Green, as well as Murphy.

“Maybe this is good for them in a sick way, that they have to get force fed,” Rivers said. “We have to throw them in there regardless and we just have to figure it out.”