The 32-year-old has claimed that he could be forced to end his lengthy playing career at the club if he remains on the bench but ultimately wants to stay.
The Spain international, who has not started a league fixture for the Blancos since January, has struggled to wrestle his starting berth back from Lopez this season, with speculation mounting that his woes could extend to the international level and jeopardize his hopes of playing in the World Cup next summer.
Casillas, who joined the club as a nine-year-old, has conceded that 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," the Roja captain 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."
Casillas is under contract at Estadio Santiago Bernabeu until 2017.