Three-time World Cup winner Pele (below) has been admitted to a "special care" unit in a Sao Paulo hospital.
The 74-year-old former Brazil forward was thought to be improving, having been taken to hospital on Monday suffering with a urinary tract infection, but was transferred yesterday.
A statement from the hospital, reported by Globoesporte.com, read: "The Hospital Israelita Albert Einstein reports that the patient Edson Arantes do Nascimento (Pele) has been admitted with clinical instability.
"To receive the best care, he has been transferred to be monitored in a special care unit.
"The hospital will update when there is new information."
Pele's personal assistant Jose Fornos, known as 'Pepito', explained the former player was moved to a more private room, with no visitors allowed.
"It will take between eight and 10 days before he can leave the hospital," he told Globoesporte.com.
Pele underwent surgery at the same hospital two weeks ago to have kidney stones removed. The issue forced the cancellation of an appearance at the Pele Museum in Santos due to "health reasons".
He has previously been under the care of the Albert Einstein hospital having had thigh surgery two years ago.
Pele, widely regarded as one of the greatest players of all time, won the World Cup with Brazil in 1958, 1962 and 1970 over a 14-year international career.