Ronaldo scored the opening two goals in the 3-0 Primera Division win at the Bernabeu on Sunday night to take his tally to 150 in 149 matches for Madrid since his world-record £80million switch from Manchester United in 2009.
However, Ronaldo did not celebrate either goal before being substituted in the second half with a minor injury.
Speaking afterwards, Ronaldo said: "I didn't celebrate the goals because I'm a little sad.
"The people inside the club know why it is. I'm not going to say anything more."
When quizzed further, the Portugal international confirmed it was for "professional" reasons and not personal.
Ronaldo denied it was anything to do with last week missing out on being named UEFA's best player in Europe, with the award going to Barcelona midfielder Andres Iniesta.
"There are more important things than that," said Ronaldo, who is now due to link up with Portugal this week for their upcoming 2014 World Cup qualifiers against Luxembourg and Azerbaijan.
Regarding his injury, the 27-year-old said: "Let's see if I recover in a couple of days because I want to play in these important games for the national team."
Ronaldo's goals against Granada helped Madrid pick up their first win of the season after they started the defence of their La Liga title with a home draw to Valencia and an away defeat to Getafe.
Ronaldo said on his club's website after reaching 150 goals for Madrid: "I'm very happy for this goalscoring run but the most important thing is the team. We got a victory and for us the league starts today."
