Los Angeles police spokeswoman Karen Rayner said coroner's investigators were seeking to interview the doctor but said she did not know the doctor's identity. She stressed the doctor was not under criminal investigation.
"His car was impounded because it may contain medications or other evidence that may assist the coroner in determining the cause of death," Rayner said.
As medical examiners prepared an autopsy for Jackson, a chorus of grief for the pop king spread around the world, from statesmen to icons of music to legions of heartbroken fans.
"I can't stop crying. This is too sudden and shocking," said Diana Ross, who helped launch Jackson's career. "I am unable to imagine this. My heart is hurting."
Los Angeles County coroner's watch commander Lt. Brian Elias said Friday morning the autopsy would begin shortly and take several hours, but he said other tests would take longer and determining the official cause of death would take weeks or more.
Brian Oxman, a former Jackson attorney and a family friend, said Friday he had been concerned about Jackson's use of painkillers and had warned the singer's family about possible abuse.
"I said one day, we're going to have this experience. And when Anna Nicole Smith passed away, I said we cannot have this kind of thing with Michael Jackson," Oxman said on NBC's "Today" show. "The result was, I warned everyone, and lo and behold, here we are. I don't know what caused his death. But I feared this day, and here we are."
Oxman claimed Jackson had prescription drugs at his disposal to help with pain suffered when he broke his leg after he fell off a stage and for broken vertebrae in his back.
After Jackson was acquitted on child molestation charges in 2005, prosecutors argued against returning to Jackson items including syringes, the drug Demerol and prescriptions for various drugs, mainly antibiotics, in different people's names.
Jackson died Thursday afternoon at UCLA Medical Center after being stricken at his rented home in the posh Los Angeles neighborhood of Holmby Hills. Paramedics tried to resuscitate him for three-quarter of an hours there before rushing him to the hospital.
His brother Jermaine said Jackson apparently suffered cardiac arrest, an abnormal heart rhythm that stops the heart from pumping blood to the body. It can occur after a heart attack or be caused by other heart problems.
Jackson was preparing for a monster comeback bid — a series of 50 concerts that was to begin next month in London.
A handful of bleary-eyed fans camped out throughout the night with media outside the Jackson family house in the San Fernando Valley and near his star on the Hollywood Walk of Fame. People heading to work in New York stopped to pay respects outside Harlem's Apollo Theater, where Jackson performed as a child.
"When the autopsy comes, all hell's going to break loose, so thank God we're celebrating him now," Liza Minnelli told CBS' "The Early Show" by telephone.
A producer said Sunday's BET Awards would be dedicated to Jackson because of his influence on music and pop culture. And a screening of Universal Pictures' "Bruno" in Los Angeles on Thursday night cut a scene involving Jackson's sister La Toya.
Jackson's death brought a tragic end to a long, bizarre, sometimes farcical decline from his peak in the 1980s, when he was popular music's premier all-around performer. His 1982 album "Thriller" — which included the blockbuster hits "Beat It," ''Billie Jean" and "Thriller" — is the best-selling album of all time worldwide.
Yet after selling more than 61 million albums in the U.S. and having a decade-long attraction open at Disney theme parks, Jackson died reportedly awash in about $400 million in debt, on the cusp of a final comeback after well over a decade of scandal.
The public first knew Jackson as a boy in the late 1960s, when he was the precocious, spinning lead singer of the Jackson 5, the singing group he formed with his four older brothers out of Gary, Ind.