Los Angeles County assistant chief coroner Ed Winter said tests on Jackson's brain are ongoing, the New York Post reported on its Web site Wednesday.
The focus will be on whether a powerful anesthetic may have contributed to the death of Jackson, 50, who suffered a cardiac arrest June 25.
"As soon as we are done with the brain, we will return it," Winter said.
Dr. Michael Baden, a forensic pathologist who has been involved in the autopsies of Anna Nicole Smith and David Carradine, said retaining the brain is essential in cases when the body is in good health a specific cause of death could not be determined.
Baden told FOXNews.com that Jackson's brain would be preserved in formaldehyde while a neuropathologist studies it over the next several weeks.
The evidence of lesions in the brain could reveal evidence of some form of damage, or injury from drugs, or a congenital abnormality, Baden said.
After the studies are complete — it could take 60 to 90 days in Georgia, Daniel said, "though it may not be as long out there" in California — the tissue is incinerated or returned to the family for burial, he said.
Jackson's death certificate, released on Tuesday, did not list a cause of death.