Ronaldo scored his 149th and 150th goals in 149 games for Madrid in a 3-0 win over Granada on Sunday evening but pointedly refused to properly celebrate at the Bernabeu.
When quizzed by journalists in the mixed zone following the Liga game, Ronaldo sparked speculation over his future by revealing he is not content with life at the Spanish champions.
"I'm sad because of a professional issue and the club know why," Ronaldo said. "That's why I didn't celebrate the goals, because I'm not happy. The people [at the club] know why.
"It's nothing to do with Andres Iniesta [winning UEFA's Best Player in Europe award]. I won't talk about this anymore and I will concentrate on Portugal for now. There are more important things [than this].
"The people at the club know about this. I cannot say any more."
It is also reported that Ronaldo was spotted crying in the Madrid dressing room following the victory over Granada.
Marca, the leading newspaper covering Real Madrid in the Spanish capital, says Ronaldo told president Florentino Perez on Saturday he did not feel wanted at the club.
The paper speculates that Ronaldo may have fallen out with some of his team-mates.