The Real Madrid forward and his Barcelona rival have effectively gone head-to-head in recent years for FIFA's Ballon d'Or, given to the player voted the world's best, after coming to dominate football's highest-profile club battle.
Ronaldo described Messi as "a great player" and admitted there is nothing he can do to sidestep comparisons between the pair.
Speaking to United States television beIN Sport, the Portuguese said: "It's not just now, it's the last five years - it's always the same.
"I cannot change that. I don't work in the press, I don't work in television. They love doing that.
"What am I going to do? I have to do my work, I have to train, I have to score, I have to play, I have to try to help my team all the time and not think about that.
"Messi is a great player. [We have] a professional relationship like I have with other players.
"I'm not a friend of him because we don't share the same dressing room and do not go out for dinner, but I respect him as a professional."
Asked if the pair could one day play together, Ronaldo mischievously suggested Messi would have to make the controversial switch from the Nou Camp to the Bernabeu for that to happen.
"Play with Messi? Why not? No problem - if he comes here we'll play together, but me going there is more difficult," said Ronaldo.