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.
Fraser Forster has rejected suggestions that Celtic's UEFA Champions League exit could hit his World Cup hopes with England.
The Parkhead goalkeeper is hoping to secure a place in Roy Hodgson's squad for the 2014 showpiece in Brazil following a series of impressive displays for his club.
Forster was handed his debut in the recent friendly international defeat by Chile and is currently regarded as back-up to international No.1 Joe Hart alongside Norwich shot-stopper John Ruddy.
With Neil Lennon's men exiting the Champions League following Tuesday's home defeat by AC Milan, and without even the consolation prize of a Europa League berth, there is no more continental competition for Forster this term.
He told the Daily Record: "This club has been fantastic for me over the past three and a bit years.
"I've loved every minute of being here since I first walked through the door. The gaffer, Stevie Woods, Billy Styles, they have all been fantastic for me.
"They've really brought my game on and helped me to develop.
"It's disappointing to be out of the Champions League but it's just a case of doing well for Celtic now and then I will have to see what happens.
"The World Cup is still a long way away and there's plenty of club football to be played between now and then.
"I don't know how damaging it is to be out of the European environment, I'll have to wait and see.
"Celtic are a fantastic club to play for and I'll take it a game at a time and not worry about the World Cup. It's still seven months away."