Jurgen Kinsmann, head coach of the South Korean men's national football team, said Wednesday he hopes China will release detained South Korean football player Son Jun-ho before Christmas, saying it was his "only one wish" for the holiday.

Son, a national team veteran, was detained by Chinese authorities in May and was placed under formal arrest in June. Few details are known about the circumstances of Son's detention, with Chinese officials only saying he is facing bribery charges. South Korean diplomats were granted consular access to the athlete in the early days but have not been able to secure his release.

Klinsmann and his players returned to South Korea on Wednesday after defeating China 3-0 in a World Cup qualifying match in Shenzhen, China.

After thanking China for their hospitality, Klinsmann expressed his hope for Son's release.

"We have only one wish for Christmas; it is to get Son Jun-ho released, because until today, they have not proven anything that he did wrong," Klinsmann told reporters gathered at Incheon International Airport, west of Seoul. "So we hope that the Chinese government will release him, hopefully before Christmas to see his family."

In a show of his support for Son, Klinsmann put the midfielder on his roster for two friendly matches in June, even though Son wouldn't be able to play.

The national team has been playing well, though, without Son's services. The Taegeuk Warriors have now won five matches in a row -- three friendlies and two World Cup qualifying matches -- and have scored 19 goals without conceding any in that stretch.

The China match was South Korea's last match of 2023. Klinsmann will now shift his focus to the Asian Football Confederation Asian Cup, which kicks off in January in Qatar. South Korea haven't won the Asian Cup since 1960.

South Korea will play Bahrain, Jordan and Malaysia in Group E, and should have little trouble advancing to the knockout stage as one of the top two teams in the group, or as one of four best third-place teams out of six groups.

But Klinsmann said he will always be wary of complacency.

"Difficult moments in tournaments can come any second. Can come in the first game. Ask Argentina against Saudi Arabia," Klinsmann said, in reference to Argentina's stunning 2-1 loss to Saudi Arabia in their first group match at last year's FIFA World Cup.

"We have to be very, very fit and focused from the first game on. And then hopefully, passing the group stage, it's the knockouts," Klinsmann continued. "In knockout games, anything can happen. You can lose in the round of 16 or you can go into the final. A tournament is a marathon, and I love tournaments. We cannot be relaxed for one second once we're in Qatar."

As part of South Korea's preparation for the Asian Cup, Klinsmann said it was "very important" for his players to compete in a hostile environment like they did in Shenzhen, with nearly 40,000 fans booing and cheering against them.

"It's very important for the players to feel uncomfortable, to play against a big crowd," he said. "This is part of football. The more they can gain this experience, the more they're prepared for this type of games."