Ronaldo was responding to Blatter's comments made earlier in the day, in which the head of world football insisted the player should be allowed to join Spanish giants Real Madrid if he wants to.
"I completely agree with the FIFA president," said the player currently resting in Portugal after undergoing an ankle operation.
He added: "The president is correct, but I do not want to say more."
Real Madrid are believed to be prepared to offer around 85 million euros for the 23-year-old and pay him nine million euros on a five-year deal.
Ronaldo, a boyhood Real fan, has consistently been linked with a move to the Spanish capital since the end of last season after scoring an impressive 42 goals last term as United won both the Premier League and Champions League.
"There is no agreement with Real Madrid and I still don't know where I will be playing next season," Ronaldo said on Thursday, adding that he will be out for "10 to 12 weeks" to recover from his operation.
Wading into the protracted wrangle over the player's future, Blatter said that the current practice of tying players to long contracts amounts to "modern slavery".