Pele admitted to special care unit in Sao Paulo
The 74-year-old was admitted to the Hospital Israelita Albert Einstein three days ago with a urinary infection.
A hospital statement on Thursday confirmed Pele had been moved to a different area of the hospital, citing "clinical instability".
It read: "Edson Arantes do Nascimento [Pele] remains in hospital.
"To receive the best care he was transferred in order to be monitored in a special care unit."
Pele underwent surgery to remove kidney stones on November 13.
Widely regarded as the finest footballer in the history of the game, Pele won the World Cup on three occasions between 1958 and 1970 and scored more than 1,000 goals in his professional career.