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.
Italian defender Davide Astori, the reported transfer target of several Barclays Premier League clubs, has signed a three-year contract extension with Cagliari.
The 27-year-old centre-back had been linked with Manchester City, Liverpool, Everton, Tottenham and, more recently, Championship club Leeds, who are now owned by Cagliari's former president Massimo Cellino.
But the defender, who made his debut for the Sardinians in 2008, has decided to remain at the Stadio Sant'Elia for another three years.
He told Cagliari's official website: "I've been here six years now and I've grown up and matured while in Sardinia.
"I wanted to show my gratitude to Cagliari. I thank president (Tommaso) Giulini: it is a decision we took together."
The Lombardy-born player spent five years in AC Milan's youth system before joining Cagliari, for whom he has made 140 Serie A appearances and scored three goals.
His commanding performances in the Rossoblu shirt have earned him wider recognition across Europe and he has also appeared seven times for Italy, scoring once against Brazil in 2013.
Cagliari director of sport Francesco Marroccu said: "We are extremely proud we have kept hold of one of our greatest professionals.
"Davide was in the last year of his contract and so the fact he wanted to renew with us shows he has great faith in the club."