Liverpool are among a number of clubs who are reported to be watching the 20-year-old, who in October was said to be stalling on contract talks in Germany.
But Hamburg remain determined to convince Son, who has scored six goals in 12 appearances this season, to sign an extension on his current deal.
Son is tied to Hamburg until the end of next season and the club's general manager, Frank Arnesen, told Hamburger Morgenpost newspaper: "As I have said, Heung-Min Son is under contract until June 2014.
"In his case, we have a huge limit. We want him to stay at Hamburg. He simply has to believe in the future of this club.
"We have the ambition to challenge for a berth in a European club competition during the next new season. We need our players."