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 striker moved to Sardinia on a permanent deal last summer after spending the previous season on loan with the Rossoblu but will now return to Brazil for family reasons.
"After more than two years with the Rossoblu, I leave Sardinia to return to Brazil and play in Santos," he told www.cagliaricalcio.net.
"It's a difficult decision, because I consider the Cagliari an important team with special fans. To them I extend my greetings.
"In Sardinia, I found love, respect, friendship from everyone: from the President Cellino, who always treated me with utmost respect, to team-mates, not to mention the technical staff as well."