The Spain international would rather play with the Portugal star than the Barca ace, and also discussed the conflict between Sergio Ramos and Jose MourinhoIker Casillas has made it clear that he would pick Real Madrid team-mate Cristiano Ronaldo over Barcelona attacker Lionel Messi if he had to make a choice between the duo.
Jose Mourinho stated after this weekend's 2-2 Clasico draw that people shouldn't compare the two as they're both from another planet, but Casillas has insisted that he prefers the Portugal star over the Argentine forward.
"I'd choose Cristiano over Messi because he's a player who gives us so much every season and he's a player I spend time with every day," Casillas told Cadena Cope.
"I know him, know who he is, know how he trains, know what he wants and where he wants to get to."
The shot-stopper also had his say on the difficult relationship between Sergio Ramos and Jose Mourinho, but refused to side with either of the two parties.
"Whose side was I on? On Sergio's, supporting a team-mate who was going through a hard time. And the boss' because he's looking out for the team.
"It's not a question of siding with Sergio or the boss but supporting everyone equally."
Ramos was benched for the Champions League win over Manchester City, but has since returned to the Madrid starting XI again.