A move to European champions Real Madrid has also been mooted for Casilla, who has one year remaining on his existing deal, but the Spaniard is keen to remain loyal to Espanyol.
"I do not want to leave this summer. My intention is to complete this season and then negotiate another deal," he told reporters.
"If I have to go, it won't be for free. Espanyol have invested heavily in me and given the economic situation, I want my club to be the only beneficiary.
"But my mind is firmly fixed on my work here. For any player, it's important to know where your future lies and I'm clear about mine."
Casilla kept nine clean sheets for the La Liga outfit last term.