Retired Brazil striker Ronaldo has thanked football fans for their support and revealed he will leave the Ibiza hospital on Monday.
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.
Ronaldo then took to his own official account on Sunday to reassure supporters and those who had sent him well-wishes, however, while confirming the trip to hospital was true.
Pneumonia affects the lungs and is caused by bacterial infection.
He has played for Barcelona, Real Madrid, Inter and AC Milan in Europe and his career ended with Brazilian side Corinthians in 2011.
Sources told Diario de Ibiza that Ronaldo was recovering well.
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During his playing career, Ronaldo was famous for his blistering pace and phenomenal goal-scoring record. He represented his country in three World Cups, including the 2002 edition, when Brazil won its fifth tournament title.
Symptoms - which include a cough and difficulty breathing - can develop suddenly over 24 to 48 hours.
Ronaldo is believed to have arrived in Ibiza for a summer holiday a few days ago before he fell sick.
In his latter years he battled with overweight because of a thyroid problem.
It can be life-threatening, especially among the elderly and those with underlying health conditions.