Spanish football expert Guillem Balague made the sensational claim in his new book "MESSI" which is being serialised by the Telegraph.
Balague wrote: " Ronaldo, perhaps as a symptom of the immaturity that marks so many footballers, thinks it necessary to put on a brave face in front of his team-mates, not be scared of Messi and to rise to the challenge. All very macho; all very false."
"And that is why, according to some Real Madrid players, CR7 has a nickname for him: ‘motherf----r’;"
Balague goes further on the subject with the claim that anyone speaking to Messi is also branded with the crude nickname.
Balague wrote: "and if he sees someone from the club speaking to Leo, he also ends up being baptised ‘motherf----r’."