The NBA's independent medical expert has concluded that Joakim Noah is physically able to play, so his 20-game suspension for violating the league's anti-drug policy will begin on Wednesday when the New York Knicks face the Miami Heat.

Joakim Noah, who was suspended 20 games after failing a test for a banned substance, has been cleared for basketball activity but will begin serving his suspension now. He will serve eight games this season and 12 games next season. Al Bello/Getty Images

Noah will miss the final eight games of the season and the first 12 games of the 2017-18 season.

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. He said on Tuesday that the supplement was not provided by the Knicks; it was something he took while trying to rehab from an injury. He apologized to the Knicks and their fans for taking a banned substance. "I made a mistake. It was a tough year for me, for this team," Noah said after returning to practice Tuesday. "... I let a lot of people down. It was a mistake. And I gotta learn from it and bounce back. This is a tough moment, and I'm going to learn from it."

Noah has not played since Feb. 4 and had arthroscopic surgery on his left knee Feb. 27 to remove loose fragments of cartilage or bone. He was originally expected to miss the remainder of the regular season, but the Knicks hoped to get Noah cleared as soon as possible so he could begin serving his suspension.

Knicks doctors cleared Noah to return to practice after meeting with him on Monday. The NBA's independent medical expert agreed with the team doctors' assessment, clearing the way for Noah to return to the active roster. Noah said on Tuesday that he has been "transparent" with the league since failing the drug test, but he did not want to provide much detail about the process. "I tried to take the right measures when I was taking supplements, and it wasn't enough," Noah said. "I don't really want to get into the details and all that. It was a long process. I think the people in the league were very cooperative. ... With these supplements, you've got to be careful, because sometimes they have other things in them that they don't say. It's a tough lesson to learn."

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 various injuries. With Noah sidelined, Kristaps Porzingis or Willy Hernangomez will likely start at center for New York for the remainder of the regular season and the beginning of next season.