Sage - whose father was Sylvester Stallone - was found dead at his apartment in Hollywood in July at the age of 36. It was later determined that he died from a heart condition.
He left behind personal property valued at $40,000 (£24,800), which his mother Madron is apparently seeking to control.
Madron has legally requested administration over Sage's estate since he did not have a valid will at the time of his death, according to TMZ.
Expendables 2 star Sylvester has not commented on this legal filing. He was married to Madron from 1974 to 1985.
He recently said that "good friends" and family are helping him through the trauma of his son's death.