The Real Madrid star was speaking on Brazilian television when the subject of performance arose.
"I have had sex several times before some games," he claimed.
"It helps you concentrate
"Not all the coaches let you have sex before a match though.
"I have noticed that in some games that I played better because I had sex before them."
Ronaldo also denied that he was dating top model Fernanda Lima - as some Spanish tabloids have reported.
"The model that everyone is talking about in Spain is only a good friend of mine," he said.
"I am not dating her at all but football players in Spain are like superstars and anything you do or anyone you see gives the press a reason for talking about you."