Smith, who won the NBA's Sixth Man of the Year award last season for his play off the bench, is recovering from off-season knee surgery and may not be fit for his team's season opener on Oct. 30.
His suspension will begin with the first game of the 2013-14 NBA season for which he is eligible and physically able to play, the league said in a statement.
Taken with the 18th overall pick by New Orleans in the 2004 draft, Smith recorded career-highs in points (18.1) and rebounds (5.3) last season.
He signed a three-year $17.9 million (£11.5m) deal with the Knicks in July.
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