The 29-year-old is refusing to rule out leaving the Santiago Bernabeu, but insists the is happy at Real.
Casillas told the Daily Star Sunday: “I am aware of the interest of both Manchester United and City.
“I’m always flattered whenever another club shows interest in my qualities as a goalkeeper. I have been at Real Madrid all my career and I still enjoy going to training every day.
“I enjoy meeting the fans too – but we all know how uncertain things are in football.
“I’m not going to say never. Right now Madrid would have to kick me out of the club before I consider a move.
“Who knows what will happen, though, if a big money offer comes in.”