The Blancos captain has hailed the recent displays of his rival goalkeeper and says that La Decima is possible this year.
Following its 2-2 draw with city rival Atletico Madrid, Carlo Ancelotti's side is one point clear at the top of the league and Casillas says that the 32-year-old shot stopper has played his part during the course of the campaign.
"Diego Lopez has had a big hand in the fact that we're top," Casillas was quoted as saying by AS. "He's doing very well. When I play, I have to do well."
The form of Lopez has restricted Casillas' appearances and the Spain international has featured only in the Copa del Rey and the Champions League for Los Blancos this season.
Nevertheless, Casillas remains positive about his situation and said that he was content to adhere to the wishes of coach Carlo Ancelotti.
"I'm fine with it," he added. "You always have to analyze what the players have contributed. You have to follow orders. Everyone wants more and that's good.
"If his decision is for me to take part in these two competitions [Copa del Rey and Champions League], I'm very happy with that. That's been the case for months now, and we can't always be on the same issue."
Despite struggling to nail down a starting berth at the club level, the 32-year old started in Spain's 1-0 friendly international victory over Italy in Madrid on Wednesday before being replaced by Barcelona's Victor Valdes at halftime.
Atletico Madrid striker Diego Costa made his first appearance for La Roja since switching allegiance from Brazil, playing the full 90 minutes, and Casillas acknowledged that it could be difficult for the forward to stake a claim to a place in Vicente del Bosque's final World Cup squad.
"It's difficult when all the cameras are focused on you," he said. "People have spoken about him for several months and, going by the conversations we had after the match, he was happy with his debut. He knows it's going to be difficult for many players to get into the 23-man squad and what he wants is to work hard. But in general he was happy."