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.
Blackburn midfielder Alan Judge has joined Sky Bet League One leaders Brentford on loan for the remainder of the season.
The 25-year-old, a summer signing from Notts County for Gary Bowyer's side, has made just 12 appearances for Rovers and has found himself down the pecking order.
"Judge is a great lad and, credit to him, he is desperate to play," Bowyer told Blackburn's official website www.rovers.co.uk.
"It isn't about the money for him - he loves playing football, but at the moment with what we have got he hasn't been able to force his way in.
"It is a move that suits all parties; it will allow him to get some games under his belt for a good team. We'll monitor his progress and hope that he does well for them."
Brentford boss Mark Warburton believes the midfielder can boost the Bees' promotion hopes.
"Alan offers us options, both wide and centrally, and I am sure he will add real value to the first-team squad in the weeks ahead." Warburton told www.brentfordfc.co.uk.