Pele is back in an intensive care unit at Sao Paulo's Albert Einstein Hospital after his health took a turn for the worst, according to ESPN Brasil.
The Brazilian football legend, 80, had been discharged from the unit earlier this week.
The hospital has provided no new information on his situation, but ESPN Brasil said Pele was re-admitted to the ICU due to acid reflux.
Pele had a colon tumour removed this month and was transferred out of the ICU on Tuesday.
The tumour was found during routine tests, removed, and sent for analysis.
After leaving the ICU, Pele said in a message to fans on Instagram that he was ready for "90 minutes, plus extra time."
Image:Zuma Press/PA Images)
He wrote: "My friends, this is a message for each of you. Don't think for a minute that I haven't read the thousands of loving messages I've received around here."
"Thank you very much to each one of you, who dedicated a minute of your day to send me positive energy. Love, love and love! I have already left the ICU and I am in my room.
"I continue every day happier, with a lot of disposition to play 90 minutes, plus extra time. We will be together soon!"
Pele has suffered from hip problems for years and cannot walk unaided. His public appearances were already being cut before the COVID-19 pandemic and since then he has made few unnecessary forays outside his house near Santos.