The 25-year-old is flying high for the North London outfit at the moment having scored 18 goals in 43 appearances in all competitions, and seven of those came in his last four outings.
However, according to The Mirror, Tottenham could be without Son for two seasons as he is required to join the South Korean Army for a spell before he turns 28.
The report adds, though, that the attacker could find a way out of it as Olympic medallists and Asian Games gold medallists are exempt from being recruited.
Son has not represented his nation at the Olympics, but he could play in the Asian Games in Indonesia later this year.
If so, the Tottenham star will miss the start of the 2018-19 season.