TAMPA, Fla. -- Former NFL receiver Vincent Jackson might have died in his Florida hotel room up to three days before being pronounced dead there, according to new information released by the Hillsborough County Medical Examiner on Thursday.

Jackson, the former Tampa Bay Buccaneers and Los Angeles Chargers wide receiver, was found dead in a Brandon, Florida, hotel room on Monday. He was 38.

The new details released by the medical examiner's office Thursday came on the same day a Jackson family spokesperson confirmed to ESPN that the family donated his brain to Boston University's CTE Center in an effort to learn more from his death.

Based on the timeline of events described in the Initial Case Summary provided to ESPN by the medical examiner's office, Jackson was located by the Hillsborough County Sheriff's Office as part of a welfare check on Feb. 12. Then on Feb. 13 and 14, the hotel staff entered his room and noticed that he was seated on the couch but slouched over.

"They assumed he was sleeping and left the room," the report said.

On Feb. 15, hotel staff again entered Jackson's room and determined he hadn't moved from his previous spot and called 911 at 11:37 a.m. There were no signs of trauma or injury, other than a small laceration on his left big toe, according to the report.

The initial report provided by the Hillsborough County Sheriff's Office did not include what transpired on Feb. 13 or 14.

Jackson had been staying at the hotel since Jan. 11. The family called the Hillsborough County Sheriff's Office on Feb. 10 to report he was missing, and a formal report was filed Feb. 11. Deputies were able to locate and speak with Jackson at the hotel on Feb. 12. After assessing Jackson's well-being, the missing persons case was canceled, per the initial report.

Thursday's updated report said there were no medications found on scene. Under "social history," it listed alcohol use, smokeless tobacco use and no known drug use. The report listed the cause and manner of his death as "pending further study," meaning it is not immediately known what killed him.

"There cannot be a rush to judgment in determining cause and manner of death," Michelle Van Dyke, a spokesperson for the Hillsborough County Medical Examiner, said in an email. "At this time, there is no timeframe for the completion of the autopsy report for Mr. Jackson, though the Medical Examiner anticipates it may take several months."

The New York Times first reported Thursday that the Jackson family had donated his brain to BU's CTE Center.

CTE, which stands for chronic traumatic encephalopathy, is a degenerative brain disease that can be caused by repeated head trauma, including trauma from sports such as football and boxing. It can be diagnosed only posthumously and in a special autopsy that examines specific portions of the brain. Researchers at BU have previously found CTE in the brains of former NFL players.

"If anything can be learned from his death that might help someone else, Vincent would want that since he was passionate during his life about impacting others around him," family spokesperson Allison Gorrell told ESPN.