All able-bodied South Korean men are obliged to serve in the military for nearly two years, making up the bulk of Seoul's 600 000-strong forces - who face off against North Korea's army of 1.3 million.
But Son was among the South Korean footballers who earned an exemption by winning gold at the 2018 Asian Games in Indonesia.
The 27-year-old's Premier League season ended even before the coronavirus outbreak spread to Europe when he broke his arm against Aston Villa on February 16, and Spurs said he returned to South Korea for "personal reasons".
Son reported to a marines camp on the southern island of Jeju for his three-week basic training, Yonhap news agency reported.