Knicks coach Derek Fisher got off scot-free Monday after the NBA concluded its investigation into his love-triangle fight with Matt Barnes in Los Angeles.

Now Fisher has to do a better job in fixing the Knicks’ triangle offense, which he finally acknowledged is broken after Sunday night’s fourth straight loss.

In an interview Monday with The Post, Charley Rosen, Phil Jackson’s confidant and his former Continental Basketball Association assistant coach, confirmed the Knicks’ system offense is lagging under Fisher’s watch, riddled with bad picks, a lack of proper movement, too much dribbling and not enough backdoor cuts.

The question is, whose fault is this? According to a source, there’s a growing sense among some players in the locker room Fisher is viewed more as a “preacher’’ and “motivator’’ than an expert in-game tactician or Xs-and-Os master.

That probably should be expected, considering Fisher has 1 ¼ seasons of coaching experience on any level. Bucks coach Jason Kidd, now on a medical leave, also is considered to be in the same boat, well behind as a tactician.

According to the source, Fisher’s assistant coaches, including Brian Keefe, Kurt Rambis and Jim Cleamons, are more versed in the strategic concepts. The source said Carmelo Anthony has come to Fisher recently to lobby for rookie Kristaps Porzingis to be more involved in the offense late in games to take the burden off him. Indeed, Porzingis had plays run for him down the stretch in Boston on Sunday.

“If you run the triangle, you have to make a total commitment to the triangle,’’ said Rosen, who writes a technical basketball column for todaysfastbreak.com. “It’s not like a part-time thing that you just use some of it. If that’s your offense, you got to commit to it. It doesn’t look like they’re really committed to it.

“They’re running it in a half-assed way. It’s not creating the kind of shots it would normally create.’’

Rosen is working on an online series detailing the Knicks’ season through Jackson’s eyes, to be published on his website after the campaign. Rosen said Jackson is still committed to the triangle.

Asked about Jackson’s mood, with the Knicks at 14-18 and falling into 12th place in the Eastern Conference, four games out of the eighth seed, Rosen said: “He enjoys wins, doesn’t enjoy the losses. He’s not a good loser.’’

Jackson last spoke to the media three days before training camp, his silence growing odder by the week. With the Knicks on the road, Jackson spent Christmas week in New York, with his kids flying into town. Jackson had promised to be more involved with the coaching staff this season, with film work.

Asked if Fisher still is learning on the job and had not mastered teaching basketball Xs and Os, Rosen said: “I think that’s valid. How much did he learn from coaching a team that won 17 games? What he did do last year was kept them playing hard, a monumental accomplishment.’’

Fisher wasn’t pleased with the offensive flow Sunday, when the team shot 37 percent. Unsolicited, he said the offense is not being run with enough commitment. Of the loss, Fisher said, in part: “It was more about our inability to work offensively as a group. We have to find a way to play offense together, and it will make it easier and allow everyone to contribute.’’

Because of the stigma developed last season over the triangle, Fisher rarely talks about it with the press.

“I don’t know if he’s not harping on them or they are resistant,’’ Rosen said. “It’s 32 games. They should be running it better, unless Fisher isn’t fully committed to it.

“I see the weak-side picks are awful. They are loose. Nobody’s headhunting or looking for somebody. It’s just very, very loose.’’

Rosen, one of the game’s staunchest triangle advocates, had a laundry list of things he doesn’t see happening, including the big men not cutting to the free-throw line where they can help out a wing player with the ball.

Though the Knicks lead the league in post-ups, using Arron Afflalo and Carmelo Anthony, they aren’t getting enough out of them. Rosen said Porzingis, even though he has gotten stronger, isn’t “holding the space in the low post. He gets pushed out, and it ruins the spacing.”

Center Robin Lopez, according to Rosen, is holding his space in the post, but “has to relearn his footwork,” saying that has caused a lot of his off-balance shots in the paint.

Finally, Rosen sees too many double-teams on Anthony, which wouldn’t occur if the triangle was crisper.

“It should be difficult for teams to double someone like Melo,’’ Rosen said. “If it’s functioning and Joe Blow is designated to double Melo, Joe Blow should never know where [Joe Blow] will be.’’

On Sunday night, Anthony didn’t want to hear about the triangle when told about Fisher’s remarks.

“I don’t know where he’s coming from with that statement,’’ Anthony said. “I’d rather him get in the gym with us and show us what he’s talking about.’’