Joakim Noah hasn't been close to the defensive leader the Knicks expected

NEW YORK --  When the New York Knicks completed their biggest free agent signing of the offseason, they thought they had discovered the elixir to solve their defensive woes.

Not so fast.

Joakim Noah has been nothing short of a disappointment during his short time in The Big Apple. The former Chicago Bulls center was given big money (four years, $72 million) to anchor the team’s porous defense, but he’s been anything but reliable.

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During Monday’s loss to the Oklahoma City Thunder, Noah was repeatedly outmuscled by Enes Kanter and grabbed just three rebounds. The Thunder easily got to the basket time and again, converting on 12 of 16 second-chance baskets for 28 points. New York was crushed on the defensive glass, too.

Russell Westbrook even was able to box out Noah and Co., to the tune of 18 rebounds.

The 31-year-old wasn’t brought in for his scoring ability -- he had just two points Monday -- and the injury concerns were no secret. Noah has already missed three games with various ailments, including Wednesday’s win over the Minnesota Timberwolves (sprained ankle).

“We got manhandled. It’s tough,’’ Noah told reporters Monday, admitting the Thunder’s ability to out-rebound the Knicks was the difference. “I want to play better, obviously. I know personally I have to play better for this team to get to where we want to get to.”

Noah came through with some nifty passes from the key as he helped the offense flow, but that’s not what he’s being counted on to do. He’s in New York to do the dirty work: to help Kristaps Porzingis patrol the paint and protect the rim. And to be a locker-room leader.

Knicks coach Jeff Hornacek has limited Noah’s minutes in crunchtime this season, opting for smaller lineups and sometimes even rookie Willy Hernangomez. When the Knicks reeled off perhaps their two biggest victories of the season -- wins over the Portland Trail Blazers and Atlanta Hawks -- Noah was missing from the lineup as he battled a stomach virus.

Kyle O’Quinn was effective in his stead, and many media members wondered if Hornacek would stick with the former Orlando Magic big man as his new starting center.

Noah, though, returned to the starting five he was supposed to solidify. He scored in double digits only once this season, a return encounter in Chicago (a win). It’s the Knicks’ poor defense, though, where it’s readily apparent Noah hasn’t been a difference-maker.

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New York is tied for seventh-most points allowed per game in the NBA (106.5). The ex-defensive player of the year is the leader of the D and the one who is depended on to ensure everyone is in position in and out of sets.

“I don’t want to say it’s a struggle,’’ Carmelo Anthony said. “I think he is trying to come back and figure it out. It’s hard being out and coming back and trying to fit in. It is going to take some time for him to get back to himself.’’

The Knicks hope that time comes soon. If not, they’re likely looking at yet another free agent bust.