A woman in her 20s known by her surname Yang was indicted earlier this year for threatening to make her pregnancy public and receiving 300 million won ($205,000) in return for her silence, after which she tried to get a further 70 million won.
A man in his 40s was also indicted for conspiring with her.
The Seoul Central District Court sentenced Yang to four years in prison and the male accomplice to two years in jail, Yonhap reported.
The defendants used Son's fame and his "vulnerability" to the type of crime they were committing, causing significant mental anguish for him, the court was reported as saying in the ruling.
Yang never confirmed the identity of the father of the child she was carrying, the court reportedly said.
Son's representatives could not be reached for comment. His agency has previously said Son had known the woman but had received a demand for money with fabricated materials, according to South Korean media.
The public affairs judge at the court did not return phone calls seeking confirmation on the sentences. A court official declined to comment. The contact information for the defendants' lawyers was not immediately available.
Son moved to MLS team Los Angeles FC from Premier League side Tottenham Hotspur earlier this year.