Phil Jackson’s offseason just keeps looking worse.

Joakim Noah, Jackson’s top target in free agency last summer and the recipient of a four-year, $72-million contract, had arthroscopic surgery on his left knee to remove a loose body on Monday. His disappointing first season as a Knick likely is over.

Earlier in the day, Brandon Jennings — who Jackson had said could be a Sixth Man of the Year candidate after he signed a one-year, $5-million deal — was waived. The Knicks signed undrafted rookie guard Chasson Randle to fill Jennings’ spot.

Randle, a Knicks training camp invite, is signed for the remainder of the season, with a partially guaranteed team option for next season. The Knicks hope to develop Randle, who played for Stanford and is well-versed in the triangle offense. Ron Baker, another undrafted rookie, and Randle will back up Derrick Rose.

Jeff Hornacek said he doesn’t expect the Knicks to waive anyone else. He bristled at the notion that they’re throwing in the towel for a better draft pick and preparing for next season.

“Who says we’re trying to lose?” Hornacek said. “As a team, we’re not thinking about losing. If that’s what it comes down to and then we get a different draft pick, we’ll worry about it then.

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“We’re still trying to win. Because Brandon was waived doesn’t mean that we’re not trying to win these games. We feel Ron Baker can fill right in.”

The Knicks are in 12th place in the Eastern Conference, 4 1⁄2 games out of the last playoff spot. So their odds are long, as are Noah’s chances of playing again this season.

Noah will be re-evaluated in three to four weeks, the Knicks said. Considering only 6 1⁄2 weeks remain, Noah’s season could be done.

“If it turns out that way, he can take all that time and the summer to get himself back right,” Hornacek said. “He’ll have a nice long stretch of getting back healthy.”

Jackson viewed Noah as a perfect fit at center in the triangle and to anchor the Knicks’ defense, but the former Defensive Player of the Year never lived up to his expectations.

Noah, who is averaging 5.0 points and 8.7 rebounds in 46 games, has battled various injuries, including a hamstring issue that kept him out of the last seven games. Hornacek said Noah woke up a few days ago with soreness in his knee. An MRI revealed a loose body.

Hornacek wouldn’t commit to Noah being the starting center next season. He said there will be a competition in training camp.

Parting with Jennings was a mutual decision. Jennings, whom the Knicks tried to move before last week’s trade deadline, was frustrated with losing, his role and the offense. Hornacek said Jennings wanted to play more minutes.

Jackson confidant Charley Rosen wrote in an Internet article Sunday that Jennings “is another player who resists the triangle” and is “a profound disappointment.” The Knicks will emphasize running and mastering the triangle for the remainder of this season.

“Brandon obviously wanted to play more minutes here,” Hornacek said. “With Derrick out here, made it awfully tough. Maybe this gives him an opportunity to get somewhere where he can play some more minutes.”

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Jennings needs to be signed by Wednesday to be eligible for the playoffs. The Wizards reportedly are leading candidates to land him.

“Thanks to my teammates and the organization,” Jennings tweeted Monday morning. “Playing in the Mecca was an amazing experience and I’m looking forward to being back on the court soon playing the game that I love.”

Rose said he spoke to Jennings before he left. “I talked to him,” said Rose, “and he seemed like he was on a mission.”

Randle played well in camp and the preseason before fracturing his orbital bone. He likely would have made the Knicks if not for that, but they kept Baker.

After he averaged 20.7 points in 19 games for the Westchester Knicks, the 76ers signed Randle to two 10-day deals. He averaged 5.3 points in eight games before being waived last week.

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“Chasson, we really liked in training camp,” Hornacek said. “We were surprised no one picked him up earlier. So now he’ll be in the mix. Young player we can develop. He knows the system, so he should be able to jump right in.”

Said Randle, “Super-excited to be back here in New York. The opportunity here is just great. It feels like home.”