It’s not every day an NBA GM cries after trading a player, as Sam Presti cried after shipping Jeff Green to Boston. But that’s the effect Green left in Oklahoma City. By all accounts, he’s a wonderful teammate and valuable locker room presence. Even those Thunder fans who questioned Green’s efficiency tended to hold a place in their heart for the combo-forward; he plays hard, plays unselfishly, and has never caused anyone to question his motives.

Landing in Boston, Green will have a better opportunity to win an NBA championship this season. But he also goes from a third option to a 6th man, from a player averaging 37 minutes per game to one who played 37 minutes total during his first two games in Boston. Even for such a well-intentioned young man — someone who encouraged Presti to say, “I have unbelievable respect for [Green] as a player and a person” — Green’s diminished role must have some effect, right?

Don’t get me wrong: I understand Green’s opportunity in Boston. Instantly, he became a part of a championship contender, a status Oklahoma City is still probably at least a year or two away from achieving. He gets to learn from Kevin Garnett, a one-of-a-kind rabid human who cares only about winning, as well as Ray Allen and Paul Pierce, two consummate professionals who have sacrificed statistics to play for a winning team.

But, for the first time in his career, Jeff Green’s a backup. A valuable backup, indeed, but a backup nonetheless. After Monday’s game, a reporter spoke to Green about whether it gave him confidence to play in the fourth quarter. He didn’t even play the whole fourth quarter, either. Just a few minutes here and there. Keep in mind, Green averaged more than 37 minutes per game in Oklahoma City. He has ALWAYS played in the fourth quarter.

“It’s cool,” he told CSNNE. “That shows that [Rivers] has a lot of faith in my game, allowing me to be out at the end of games.”

But, again, he had ALWAYS played in the fourth quarter. Always. This is the first time a team hasn’t expected Green to play major minutes. The first time he’s been somewhat of an afterthought. The first time he has ever come off the bench since his rookie season. Even then, Green started 52 out of 80 games played.

I’m not trying to say Green’s furious with his role — he’s a team player, and smart enough to realize, “Well, I’m playing behind Paul Pierce and Kevin Garnett; I don’t deserve to start.” But there will most definitely be an adjustment period, as Green becomes accustomed to his new niche, a niche he’s never played before in the NBA.

A columnist for the Oklahoman, Berry Tramel, watched Green’s first two games as a Celtic and came away thinking Green looked tentative. “Jeff Green looks lost in Boston,” he wrote, citing how Nenad Krstic — against all odds — has been Boston’s true prize from the trade so far. Granted, the pair has played only two games as Celtics. Granted, Green already does things nobody else on the team can do — like seamlessly swing from small forward to power forward, and even, against the Jazz, shooting guard for a little while. Granted, KG has already written poems (not literally) about Green’s versatility. But the transition for Green has not been flawless. Not yet, at least, though it does not take an advanced scout to see the potential.

As Green continues to grow into his new role, Doc Rivers’ mind churns with ways to maximize his new toy’s talents. He has already tried Green in a number of different lineups. He has integrated Green with the starters, and he has played Green solely with bench players. He has played Green at three different positions, with who-knows-how-many combinations of players surrounding him. Rivers admits he still does not know how to utilize Green, and so he tries lineup, after lineup, after lineup. You get the feeling Rivers loves having Green’s versatility, and that makes sense — Green gives the Celtics lineup flexibility they haven’t had since the days of James Posey. But you also get the feeling Rivers wishes he could fast-forward through the “figure each other out” process and know exactly how to use his newest acquisition.

Ultimately, Green should learn how to mesh with his new team and Doc Rivers should learn how to use him. But for now, the acclimation continues.