Another one of Michael Jackson's doctors is in the hot seat.

Lawrence Koplin, a Beverly Hills plastic surgeon, is being investigated in MJ's death. Coroner Assistant Chief Ed Winter went to the doc's office on Wednesday and later told reporters he was looking for the King of Pop's medical records.

"We're cooperating with the coroner's office and we have no comment at this time," a rep for the physician's office told People.com.

Joining Dr. Conrad Murray and Dr. Arnold Klein, Dr. Koplin's treatment of the singer is in question -- and cops are, no doubt, searching for info on what drugs were prescribed to Michael through his office.

Though toxicology reports on MJ were scheduled to come back by the end of this week, the coroner told the Associated Press that it's looking like they are going to be delayed.