Arnie Klein -- Bankrupt MJ Doc Dumping Laguna Beach Mansion

Dr. Arnie Klein -- Michael Jackson's now-bankrupt former dermatologist -- has already lost his Hancock Park mansion ... and now he's kissing his enormous Laguna Beach mansion goodbye.

The cash-poor Klein has listed the 3,500 sq. ft. property for $6.63 MILLION. And get this ... Klein tried to unload the property last year, listing it for a cool $12 mil.

Klein's fall has been breathtaking. He was once the premiere dermatologist in Bev Hills ... the dermatologist to the stars, including MJ, Elizabeth Taylor and Cher.

Klein's medical practices were put under a microscope after MJ died. The doc was fueling MJ with huge quantities of prescription drugs, including Demerol -- he injected MJ with Demerol 51 times in the 3 months preceding his death.