Sources close to the star have said that a lawyer could submit the document to the Los Angeles Superior Court as early as this week, The Wall Street Journal reports.
It is believed that the will divides Michael's estate between his mother Katherine, his three children and one or more charities, but does not include his father Joe, with whom he had a difficult relationship.
Jackson family lawyer L. Londell McMillan said: "No will has been presented to family or us. We will review any will when we see it."
Reports have suggested that Michael's parents told the courts on Monday that their son died without a valid will.
In a 1993 interview with Oprah Winfrey, Michael claimed that he had been emotionally and physically abused by his father during his childhood.
Speaking to Louis Theroux for the BBC in 2003, Joe admitted to striking his son but denied ever beating him.
Joe said: "I whipped him with a switch and a belt. I never beat him. You beat someone with a stick."