The Spain international has made just four appearances so far this season, although he played a key role in helping Real secure a 2-2 draw with Juventus in the UEFA Champions League on Tuesday.
Casillas has been out of favour since fracturing his hand in January, allowing Diego Lopez to establish himself as Real's first-choice keeper.
The 32-year-old has been linked with a move away from the Bernabeu, but Casillas has no immediate plans to leave the club.
"I'm staying here in January, June and until the end of my contract," he said.
"But I do not know what will happen in a year, two or three."
All of Casillas' appearances for Carlo Ancelotti's men have come in the Champions League, and the shot-stopper admitted that he is finding it difficult to adapt to the rotation policy.
"You need to be at the highest level so that they trust me," he added.
"It is not easy because you play every two weeks.
"It is difficult to maintain concentration, but my team-mates help."
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