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.
The 22-year-old Belgian player has been unable to earn a regular first-team place at Stamford Bridge, and the arrival of Nemanja Matic from Benfica means he will be sacrificed by manager Jose Mourinho.
De Bruyne had a successful loan spell with Wolfsburg's Bundesliga rivals Werder Bremen last season, and is now poised to make a permanent switch to Germany.
German reports suggest Wolfsburg will pay around 20million euros (£16.7million) for the player.
Wolfsburg are on a mid-season trip in China, but sporting director Klaus Allofs told German broadcaster NDR: "Kevin is in Wolfsburg. We hope that everything so far is going to plan."