Dr. Arnold Klein's office manager -- who claims he was Michael Jackson's lover -- is facing such intense death threats that he's moving from place to place ... hiding out from angry MJ fans.

Dr. Arnold Klein's office manager -- who claims he was Michael Jackson's lover -- is facing such intense death threats that he's moving from place to place ... hiding out from angry MJ fans.


A 情報源 close to Dr. Klein and Jason Pfeiffer tells TMZ incensed Jackson ファン have walked right up to Pfeiffer's ホーム and knocked on his door -- and they've also tracked him down at his friends' houses.

Since Jason went public last week with allegations of an affair with Michael, we're told violent and homophobic threats have poured into Dr. Klein's office によって phone, fax, and email. According to the 情報源 one voicemail said, "I'm gonna put a bullet in your heads."

Klein and Pfeiffer have hired bodyguards, and reported the threats to the FBI. We're told Pfeiffer is currently at a private location with friends.