Jose Mourinho's No.2 believes the two talismen are from out of this world, while their determination to be the best sees them push one another to new heights
The Barcelona star broke Gerd Muller's long-standing goalscoring record of 85 goals for club and country in one calendar year with his double against Betis at the weekend, while Ronaldo helped Madrid to the Liga title last term with 46 goals in 38 appearances.
"As I think the boss [Jose Mourinho] said after the Barcelona game, we are talking about players who are from a different galaxy and each of them is feeding off the other," Karanka said at a press conference.
"One beats a record and the next year the other one goes one better. Their respective clubs are fortunate to be able to enjoy their talent and exploit it to the utmost."
Ronaldo and Messi have both been nominated for the 2012 Fifa Ballon d'Or, with Andres Iniesta being the third candidate to win the prestigious individual award.