Ronaldo has scored 30 goals in 29 games in all competitions this season but doubts over his form have been raised in 2016, with the Portugal captain failing to find the net in four of his last six league matches.
The 31-year-old was disappointing in Madrid's 2-1 win away to Granada on Sunday but Aduriz, who has enjoyed strong form for Athletic this term, says neither Ronaldo nor Lionel Messi should be called into question given their records.
"Can Cristiano be questioned? It seems like an insult to me. We can't question him for anything in the world," he said, as quoted by AS.
"We're very spoiled [with Messi and Ronaldo]. Their numbers are astronomical."
Aduriz's own form has led to growing calls in Spain for Vicente del Bosque to include him in the squad for Euro 2016, and the head coach stated last month that he could not rule any player out of contention.
But the former Valencia striker, who turns 35 this week, says his focus is firmly on continuing to perform well for Athletic in their fight for the European spots.
"It's not only me who can answer this question. The important thing is to do well for the team and what has to happen will happen," he added.
"Of course there are players and strikers who are doing incredible things. The level is very high and that's good for La Liga and everybody.
"I have a lot of respect and admiration for the coach."
