The closed-casket service for the 36-year-old actor, director and producer is to take place Saturday at St. Martin of Tours Catholic Church.
Sage's mother, Sasha, has requested donations be made to the organization Autism Speaks in lieu of flowers, "ET" said Tuesday. Sage's younger brother, Seargeoh, is autistic.
A spokesman for the Los Angeles County Coroner says the cause of Sage Stallone's death will be determined in about two months after toxicology tests are completed.
Police investigating his death have said there were no signs of foul play, and an autopsy conducted Sunday proved inconclusive.
The New York Post has reported a prescription drug overdose is suspected but said it is unclear whether it could have been accidental or a suicide.
Sage Stallone appeared alongside his action film icon father in the 1990s movies "Daylight" and "Rocky V."