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Saito, a reserve athlete who had not yet competed, was provisionally suspended after testing positive for masking agent acetalozamide, CAS said, adding that a final ruling would be issued after the Games.
Masking agents are often used to cover up banned performance-enhancing substances.
This is the first doping case during the testing period of the Olympics in South Korea and comes as Tokyo prepares to host the Summer Games in 2020.
"The athlete accepted on a voluntary basis to be provisionally suspended and to leave the Olympic village," CAS said.
"As a consequence, the athlete is provisionally suspended from competing at the Pyeongchang 2018 (Olympic Games) and at any future ISU (International Skating Union) competition pending the resolution of this matter."
The Japanese Olympic Committee is to hold a news conference later in the day.
Doping cases are rare among Japanese athletes and this is the first for the country at a Winter Olympics.
Last month, however, sprint canoeist Yasuhiro Suzuki admitted to spiking a rival's drink with an anabolic steroid to scuttle his Olympic dream, and was banned for eight years.
He now faces a lifetime ban from the Japan canoe federation.