The former Real Madrid youth product is widely regarded as one of the most talented stoppers in La Liga, with his performances over the last 12 months drawing a host of outside interest.
However, the 27-year-old has claimed that his "intention" is to remain in Barcelona.
"I'm not at all worried. I have a year on my contract and I'll still be here for that time and hopefully even more," he told reporters.
"My intention has always been to stay here because when I've been out and things didn't go well, I've always had the support of the club."
Casilla has been with Espanyol since 2008.