Cardiff will allow long-serving Kevin McNaughton to leave this summer along with Danny Gabbidon and Nicky Maynard.
Highly-rated Atletico Madrid midfielder Saul Niguez has signed a new five-year contract.
Hamburg sporting director Frank Arnesen is confident forward Son Heung-min will remain with the Bundesliga side for the foreseeable future and hinted the South Korean is in line for a new contract.
The 20-year-old has been linked with a move to the English Premier League after a string of impressive performances for Thorsten Fink's side.
Son has netted seven league goals in 18 games this season, with his latest coming in last weekend's 3-2 win over northern German rivals Werder Bremen.
Rumours have circulated that Hamburg's financial troubles could force the sale of one of their biggest assets. Arnesen, however, sees it differently.
"I am sure that we can satisfy Son financially," says Arnesen in German newspaper Bild. "Of course we have our limit. But Son is 20-years old, he is a very great talent. You have to pay for it. So I have no problems. "