The 27-year-old is reported to have been a long-term target for Arsenal.
Arsene Wenger is back in the market for goalkeeping cover after losing Lukas Fabianski on a free transfer to Swansea City.
Arsenal are, however, likely to face competition for Casilla’s signature from Real Madrid – as they still own 50 per cent of a player brought through their academy system.
A return to Santiago Bernabeu has been mooted as Casilla has just one year remaining on his contract and Real are aware that they could end up missing out on the player and a fee if he becomes a free agent.
Espanyol’s first-choice shot-stopper is in no rush to take on a new challenge, though, and claims he will only be moving on if his current employers decide to cash in.
Casilla told a press conference on Thursday: "I do not want to leave this summer.
"My intention is to complete this season and then negotiate another deal.
"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."