The NBA has suspended New York Knicks center Joakim Noah for 20 games for violating the league's anti-drug policy, it was announced Saturday.

The suspension will start when Noah -- who has not played since Feb. 4 and had arthroscopic surgery on his left knee Feb. 27 to remove loose fragments of cartilage or bone -- is "eligible and physically able to play" in either a regular season or playoff game, the NBA said. The suspension would then carry into the 2017-18 season.

Noah was initially expected to miss the rest of the season, but New York will likely try to have him return as soon as possible to start the clock on the suspension.

The Knicks expected to evaluate Noah later next week to determine if he'll be able to return to the court this season. Knicks coach Jeff Hornacek told reporters in San Antonio on Saturday that Noah hasn't yet started on-court work. The Knicks have nine games remaining on their schedule following Saturday's game against the Spurs, so Noah will serve at least 11 games of the suspension next season.

Knicks center Joakim Noah will miss the team's next two games for personal reasons. Michael Reaves/Getty Images

The National Basketball Players Association announced Saturday that neither Noah nor the union would appeal the suspension.

"We believe that this isolated occurrence was a regrettable mistake," the union announced in a statement. "Joakim has offered his deepest apologies for this infraction."

Noah, 32, tested positive for an over-the-counter supplement -- selective androgen receptor modulator LGD-4033 -- that is banned under the NBA's current collective bargaining agreement.

LGD-4033 is defined as a "non-steroidal, selective androgen receptor modulator that, much like testosterone, can create anabolic activity in muscles and bones" and "provides many of the muscle-building and therapeutic benefits of testosterone, without the same level of troublesome side effects," according to elitefitness.com.

The NBPA said Noah "did not intentionally or knowingly" violate the CBA and that he was "completely forthcoming and cooperative" throughout the investigation.

Noah could have contested the suspension under the new CBA, which takes effect on July 1, arguing that it was an "unintentional ingestion." But Noah will not have that opportunity in this case.

The Knicks signed Noah to a four-year, $72 million contract over the summer with the hopes that he could be a defensive anchor for the club. Noah has performed well below expectations, missing time throughout the season because of a hamstring injury.

Noah is averaging 5.0 points and 8.8 rebounds in 46 games (all starts) this season. Knicks president Phil Jackson signed Noah with the idea that he would anchor New York's defense. But the Knicks struggled on that end of the floor even when Noah was healthy, ranking in the bottom third of the NBA in defensive efficiency for much of the season.

Noah's suspension may force the Knicks to alter their offseason plans and look for a veteran center in free agency. The club can also weather Noah's absence internally. Rookie Willy Hernangomez, second-year big man Kristaps Porzingis and veteran Kyle O'Quinn have started at center in place of Noah this season.

Hornacek earlier this season left open the possibility that Porzingis or Hernangomez would start next season at center, regardless of Noah's status. The coach suggested that the position would be open for competition in training camp.

Noah will forfeit between $2 million and $3 million in salary during the suspension. The exact amount is unclear because the formula in the new CBA for lost salary during a suspension results in lower monetary penalties for players.

ESPN's Ian Begley contributed to this report.