Beijing's foreign ministry said in May that the 31-year-old had been detained "on suspicion of accepting bribes by non-state employees", without giving details.
South Korean media reported that Son was being held in the northeastern province of Liaoning but there has been no news of his fate since. Son had been with Chinese Super League side Shandong Taishan since 2021 and played in three of his country's four games at the 2022 World Cup in Qatar.
"Now we have only one wish for Christmas," German great Klinsmann told reporters after landing in South Korea following Tuesday's 3-0 World Cup qualifying win away in China.
"That is to get Son Jun-ho released because until today, they have not proven anything that he did wrong. So we hope that the Chinese government will release him, hopefully before Christmas, to see his family," Klinsmann added.
In a show of support, Klinsmann included Son in his squad for two friendlies in June despite his detention. The Korea Football Association told 'AFP' at the time that it had sent officials to China to seek Son's release, but the player's lawyer was "reluctant" to speak to them.
Asked about Son's case on Thursday, Beijing's foreign ministry said China was a "country under the rule of law". China "handles cases strictly according to law and protects the legitimate rights and interests of the parties involved," spokeswoman Mao Ning said.