The 51-year-old has been diagnosed with advanced lung cancer, and is now resting at mother Jackie Stallone's home in Beverly Hills, reports the Sunday Express.
Stallone's mother said of the siblings' relationship: "She has been the little angel he's tried to guide through life."
Stallone, known for his action roles in Rambo and Rocky, has had several recent projects in the works, including a recently-wrapped sequel to The Expendables and a new film called The Tomb in which he is to star opposite Arnold Schwarzenegger.
The film is in pre-production, and is scheduled to start shooting later this year.
The actor's father Frank Stallone also died at the age of 91 in July, after suffering from prostate cancer.