Ronaldo and Messi are widely regarded as two of the best players in the history of football, and the La Liga duo have broken a number of records at their respective clubs over the last few seasons.
Ronaldo has said that he is "not Messi's friend", but the Portuguese has said that his supposed long-running rivalry with Barcelona's Argentine international is a myth.
"I'm not Messi's friend, but we're fellow professionals," Ronaldo told Fox Sports. "We've shared many moments at award ceremonies in the last 10 years, and I have a very good relationship with him.
"We don't eat out together, but I respect him. He's a fellow professional of mine, not a rival. It's one more issue for the press, which want to sell papers and do their business.
"Watching Messi play? Of course I like it, I like to watch all the good players and he's one of them, he's a 'crack'. I enjoy watching him play. How can I not like a person who hasn't done anything wrong, on the contrary?
"When Messi is asked about Cristiano, he also speaks well of me. My relationship with him is cordial and we respect each other."
Ronaldo and Messi, who have won seven Champions League titles between them, have dominated the Ballon d'Or over the last nine years.