The 20-year old South Korean striker is attracting the interest of Liverpool but former Tottenham ace van der Vaart feels he is better suited to become a key player with Hamburg before making the leap into the Premier League.
"I can just say that he needs to play on for this club," the Dutchman told Sport-BILD of Son who has netted six goals this season.
"Of course it is flattering to have a club like Liverpool enquiring. But over here he has the faith, over here he is playing regular first-team matches.
"Moving on would be way too early."