Former Brazil star Ronaldo was admitted to hospital in Ibiza last Friday with a case of pneumonia.
"Friends, I had a very strong flu in Ibiza and I had to be hospitalised on Friday but everything is in order", the legendary Brazil forward said on Twitter.
Respected island daily Diario de Ibiza said he had asked for a transfer to a private hospital called Clinica Nuestra Senora del Rosario just before midnight the same day.
It quoted hospital sources as stating that Ronaldo was still in intensive care but that he was making good progress.
He is a regular traveler to Ibiza and also owns a house in the island.
Ronaldo retired from football in 2011 following a hugely successful career which featured stints including Real Madrid, where he is a club ambassador.
He is believed to have arrived in Ibiza for a summer break a few days ago.
Pneumonia affects the lungs and is caused by bacterial infection.
Throughout a prosperous career, he scored 62 goals in 98 worldwide appearances for Brazil.
Ronaldo scored 62 times for Brazil, including both goals when they beat Germany in the 2002 World Cup final.
Symptoms - which include a cough and difficulty breathing - can develop suddenly over 24 to 48 hours.
Ronaldo had taken part in the 2018 World Cup opening ceremony in Russian Federation.
During his glittering career Ronaldo won the FIFA World Player of the Year award three times, in 1996, 1997, and 2002.