A third positive drug test triggers a five-game suspension.
Smith averaged 18 ppg last season and was rewarded with a new $18 million three-year contract by the Knicks.
This is Smith's fifth suspension during his nine-year NBA career, but the first for drugs. He was docked a game during the recent playoffs against Indiana after being charged with a flagrant foul.
It's been rumored that the heavily-tattooed baller has dated Rihanna.