The legendary striker, who retired from the game last year, posted a picture of himself receiving treatment on Twitter on Wednesday after picking up the illness from a mosquito
The now-retired 35-year-old made the announcement after posting a picture of himself receiving treatment for the disease on Twitter.
"Good morning to you. I have started the year with dengue,” wrote Ronaldo, who had been celebarting the new year in Trancoso, Bahia. “Thank you for [your] caring. I'm in recovery.
"I was released [on] Tuesday night. Now for treatment and rest and to get well soon!!!"
Dengue is transmitted by several species of mosquito and can, in a small proportion of cases, develop into a life-threatening condition. Though mosquitos can pass the disease on to people, it is not infectious among humans.
Ronaldo, the all-time leading scorer in World Cup history with 15 goals, called time on his illustrious playing career last year after struggling for a long time with weight problems and the effects of a succession of injuries.