The 29-year-old has spent his entire playing career at the Santiago Bernabeu and is in no rush to leave the club having come through the ranks as a teenager some 12-years ago.
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Speaking to the Star, Casillas said: “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.”
Casillas is currently in South Africa as part of Spain’s World Cup squad who face arch rivals Portugal on Tuesday, but admits he could be open to a move to either Old Trafford or Eastlands should new Real manager Jose Mourinho decide to cash in on his stalwart.
“I'm not going to say never. Right now Madrid would have to kick me out of the club before I consider a move,” Casillas continued.
“Who knows what will happen, though, if a big-money offer comes in.”
Mourinho has already expressed his desire to keep Casillas in Madrid but, according to some Spanish media reports last summer, Roberto Mancini's side have had an offer rejected and could return to test his resolve as he looks to remould the flagging fortunes of the Galaticos.
Casillas has a whopping seven-years remaining on his contract having penned a deal to finish his career at the Bernabeu in February 2008.
Manchester City appear to be well stocked on goalkeepers, with the vastly experienced Shay Given backed up by England international Joe Hart, who spent last season impressing on loan at Birmingham City.
Sir Alex Ferguson's need for a new No.1 stopper appears to be the greater, with 39-year-old Dutchman Edwin van der Sar expected to retire in a year's time.
The Red Devils sold highly-rated English custodian Ben Foster to Birmingham earlier this summer, while Tomasz Kuszczak is not thought to be considered a long-term first choice option for the Old Trafford outfit.
By James Martini
