Pele, who is 80, had previously been in hospital after undergoing surgery on a tumour on his colon.
But on Friday night, ESPN Brasil reported that Pele has re-entered an ICU at Sao Paulo’s Albert Einstein Hospital in an apparent deterioration of his health after he left the unit earlier this week.
Reuters report how the hospital and Pele’s representative in Santos said they could not confirm the news.
ESPN Brasil said the three-time World Cup winner was re-admitted to the ICU due to acid reflux.
After he had been moved out of the ICU on Tuesday, Pele posted a picture on Instagram with the message he was ready for “90 minutes, plus extra time.”
The 80-year-old is regarded as one of, if not the greatest, footballers of all time after winning three World Cups with Brazil.
He retired from football in 1977, and his health has been a source of concern to family and fans in recent years.
Pele has suffered from hip problems for years and cannot walk unaided. In 2014 he spent some time in the ICU due to a severe urinary tract infection.