The 2018 Latin America Amateur champion, who has five top-25 finishes in his last six PGA Tour starts, was due to make his second Masters start next week.
“I have tested positive for coronavirus and unfortunately I will not play ...as a result,” Niemann wrote on Twitter.
“This event means a lot to me, and I have had incredible memories playing as the LAAC champion ... I am disappointed but will do everything possible to recover quickly while keeping my family and team safe.”
Niemann, who missed the cut at the 2018 Masters, became the first player from Chile to win on the PGA Tour in September 2019 when he triumphed by six shots at A Military Tribute at the Greenbrier.
The Masters, which brings together the world’s best golfers in one of the sport’s four majors, is typically played in early April but was this year postponed to Nov. 12-15 because of COVID-19 and will be played without spectators. Reporting by Frank Pingue in Toronto; editing by John Stonestreet