Former Brazilian international and world player of the year Ronaldo has contracted Dengue fever.
The illness is transmitted by several species of mosquito and can develop into a life-threatening condition.
"Good morning to you. I have started the year with dengue," Ronaldo wrote on Twitter. "Thank you for caring. I'm in recovery.
"I was released Tuesday night. Now for treatment and rest and to get well soon!!!"
Ronaldo, 35, is the all-time leading scorer in World Cup history with 15 goals.