The former Watford boss claims that he will keep only the most suitable players for the Bluebirds' top-flight campaign in 2013-14.
"I've had to be ruthless from the very first day I came here," BBC Sport quotes him as saying. "What we are doing is for the good of the football club.
"You have to realise life changes and situations change and you have to go with change. If you don't then you're left behind. But that's not just me, that's throughout football. In end-of-season games, everybody's playing for something, whether you're in contract or going out of contract.
"You're trying to impress every time you walk over the white line so the players know they've got to be playing well to be part of something here next year, which is very exciting."
Cardiff will win the Championship title on Friday if Hull City lose to relegated Bristol City.