The experienced goalkeeper has voiced his admiration for the Portugal star and has stressed that he's eager to stay at Madrid.
The Portugal international failed to find the net in the first leg of the quarter-final tie, yet Casillas was quick to stress that the 2013 Fifa Ballon d'Or winner is Madrid's undisputed star player.
"He's a born winner and always wants more and to score more goals," Casillas was quoted as saying by the official Madrid website. "Even though he didn’t score Tuesday, the whole team knows that he is important for us and will work hard to help the team in the second leg. I’m sure that he’ll score.
"He is a cornerstone of this Real Madrid team."
Casillas then went on to discuss his future at los Blancos and insisted he is not thinking about a transfer for now, despite being behind Diego Lopez in the pecking order for La Liga games.
"I see myself at Real Madrid next season," the club captain said. "I am not planning my departure. I am only thinking about enjoying myself at Madrid."
The 32-year-old has a contract with the Liga giants until June 2017.