The two-time World Cup champion reportedly asked for a transfer to a private health facility identified as Clinica Nuestra Señora del Rosario later that night before being taken to intensive care.
The 41-year-old Brazilian was rushed to Can Misses Hospital on Friday after being diagnosed with the illness.
Here's hoping he pulls through.
Friends, I had a strong flu picture in Ibiza and I had to be boarded on Friday but it's all in order.
The former Barcelona forward provided a medical update on social media on Sunday afternoon, saying he went into hospital on Friday suffering from a bad bout of flu.
Trump authorizes doubling of tariffs on Turkey's steel, aluminum
It is host to an X-band radar, a critical part of the Western alliance's missile defence system again Iran. The lira's value fell about 13 percent against the dollar on Friday.
Ronaldo Nazario was admitted to hospital in Ibiza to be treated for pneumonia, with the former Brazil and Real Madrid great set to be discharged on Monday. "Thanks for all your support and your messages".
However the pneumonia is likely to have been triggered by an unrelated bacterial infection.
Ronaldo, who was on holiday when he was taken ill, retired from football in 2011 following a hugely successful career that featured stints at PSV Eindhoven, Barcelona, Inter Milan, AC Milan, Brazilian sides Corinthians and Cruzeiro as well as Real Madrid, where he is a club ambassador.
He scored 62 goals in 98 appearances for his country and played for some of the top clubs in Europe. Tissue swells, and it can cause coughing and breathing difficulties.
He was instrumental when Brazil won the World Cup in 2002, scoring both goals as they beat Germany 2-0 in the final.