The 41-year-old former striker tweeted that he was taken ill on Friday but hopes to be discharged on Monday.
It quoted hospital sources as saying he was still in intensive care but he was making good progress.
The former Real Madrid and Barcelona forward was said to have been rushed to intensive care in Ibiza after being struck down with pneumonia, eventually being transferred to a private hospital, Clinica Nuestra Señora del Rosario. No further information is now available about his condition.
Ronaldo, regarded as one of the world's best-ever players, owns a house in Ibiza and is a regular visitor to the island.
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The Belgian winger was simply scintillating against Huddersfield when he came off the bench in the Blues' 3-0 win, away from home. Huddersfield: Hamer 7, Hadergjonaj 7, Schindler 6, Zanka 5, Kongolo 5, Mooy 5, Hogg 6, Billing 6, Pritchard 6, Lowe 5, Mounie 6.
Ronaldo is believed to have arrived in Ibiza for a summer break a few days ago.
Symptoms - which include a cough and difficulty breathing - can develop suddenly over 24 to 48 hours. He has suffered since the end of his career with a thyroid problem that has caused him to gain a lot of weight, and back in 2012 he contracted Dengue fever and was admitted to hospital.
It can be life-threatening, especially among the elderly and those with underlying health conditions. Ronaldo scored twice in the game and was named man of the match as his side picked up the trophy for the fifth time.
It comes just weeks after the two-time World Cup victor was in Russian Federation to open the 2018 tournament, appearing on screen with the official ball and taking part in a passing routine with a local child.
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