The 34-year-old attacking midfielder spent five days in hospital after fainting during a routine medical in November. He was diagnosed with vasovagal syncope, a condition caused by a sudden drop in blood pressure, heart rate, and cerebral blood flow, which forced him to end his career.
Oscar, who won two league titles in five years at Chelsea, had a contract with São Paulo that was due to expire in 2027. The Brazilian international has not played since the incident that led to his retirement.