The 32-year-old has claimed that he could be forced to end his time at the club if he continues to be left on the bench at the Santiago Bernabeu
The Spain international, who has not started a league fixture for Madrid since January, has struggled to secure his starting place ahead of Lopez this season, while the 32-year-old's hopes of playing in the World Cup next summer may also be in doubt.
Casillas, who joined the club as a nine-year-old and is contracted to Madrid until 2017, concedes he may have to call time on his lengthy spell in the Spanish capital as soon as January.
"If a player isn't in the action then he starts to think about making a decision," Casillas told reporters.
"I’m human and I’m a footballer. I haven’t played for nine months now and it’s the same for me. I’m not a robot.
"Of course I want to stay here and win more titles with Real Madrid. I’ve been here since I was little, but there will come a day in which I have to take a decision.
"As of now my decision is to stay and fight, to struggle and play every day. If I wasn’t sure about it I would have told the president I wanted to leave in September.
"That being said, if in three months things haven’t changed and you ask me the same question, well maybe I’ll be thinking about leaving."