Lopez displaced Casillas as Madrid's No.1 under Jose Mourinho in 2012-13 and has held on to his place under Carlo Ancelotti this term.
A number of reports last year claimed that the two had fallen out with each other following their changed situation, but Lopez has stressed both goalkeepers have nothing but respect for each other.
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"I have a good relationship with Iker. A relationship can change over time, but not because the situation changed," Lopez told El Larguero. "I admire Iker and have a lot of respect for him. I have always respected him and he has never been disrespectful toward me.
"We have a normal and friendly relationship. We have respect for each other and are both loved by the fans. It's impossible to say anything negative about Iker, because I would be lying.
"If we reach the Champions League and the coach decides to play Iker, I would respect his decision."
Lopez, 32, has kept 12 clean sheets in 28 La Liga appearances so far this season.