The attacking midfielder was hospitalised for five days in November after fainting during a routine medical and has not played since.
A vasovagal syncope, caused by a sudden drop in blood pressure, heart rate, and cerebral blood flow was observed, forcing Oscar to call time on his career. He had a contract that was due to expire in 2027.
"I am ending a career here in Sao Paulo that has taken me practically to the four corners of the world," the former Chelsea and Shanghai Port player said in a club statement.
Oscar played for five seasons with Chelsea, winning two Premier League titles and the Europa League, before moving to Shanghai in 2017, where he won three Chinese Super League titles.
In 2025, he returned to Sao Paulo where he started his career. Capped 48 times for Brazil, Oscar won the FIFA Confederations Cup and played in the 2014 World Cup on home soil.