It ain't lookin' good for Dr. Arnie Klein ... Michael Jackson's dermatologist is under investigation by the Medical Board of California --  reportedly for pumping the singer full of prescription painkillers -- and now his lawyer has officially jumped ship.

Klein just posted a letter on his Facebook page, apparently sent from his former attorney -- advising Klein that he's been subpoenaed by the Board and has to appear for questioning on Dec. 15.

The letter does not explain the nature of the probe -- but according to TheDailyBeast.com, officials want to know more about allegations that Klein over-prescribed Demerol to MJ.

The Board reportedly wants to question Klein about the possibility that he self-prescribed narcotics, used false names on narcotics prescriptions, illegally handed out samples of dangerous drugs to his famous patients, and may have committed gross negligence by practicing while afflicted with multiple sclerosis.

Klein has always strongly denied any wrongdoing ... and thus far, has not been accused of any criminal conduct in the death of Michael Jackson.

As for Klein's lawyer, Herbert L. Weinberg -- dude doesn't explain why he's bailing on Arnie ... but recommends a couple of "fine lawyers" who could take over.

We called Klein for comment -- so far, no response.

Dr. Conrad Murray told police ... he had no clue what medications Michael Jackson had been prescribed by other doctors -- and although he knew it was going on ... Murray says MJ never told him he was seeing other doctors.

In the police interview from June 27th 2009 -- two days after MJ died -- Murray cites Dr. Arnold Klein as one doctor who regularly prescribed MJ drugs behind Murray's back.

According to Murray, MJ's production team often complained about the singer's visits to Klein -- insisting Michael's worst days on set were after he had been to Dr. Klein's office ... about three times a week.

During the taped interview -- played in court today -- Murray told police ... "When [Michael] came back [from Klein's office], he was basically wasted and required 24 hours for recovery."

Murray claims the only evidence of doctor-shopping he saw was a smattering of prescription pill bottles by the singer's bedside, bearing other doctors' names.

But Murray insists ... Michael never spoke about it.

Dr. Arnie Klein's got some fall shopping to catch up on in Beverly Hills -- because TMZ has learned, the Michael Jackson estate just REJECTED the good doc's claim to return his old, $10,000 jacket.

TMZ broke the story -- Klein says he loaned Michael Jackson a $10,000 Gianfranco Ferre jacket before the singer died, but MJ never returned it.

Klein filed a claim against Michael's estate back in February 2010 to get it back -- and yesterday, the estate finally got around to giving him an answer ... go fly a kite.

But the estate didn't just tell Arnie to buzz off -- according to the legal docs, the estate also rejected a former lawyer's $3 million bill, an old accountant's $60,000 bill ... plus an additional $354,230 in other claims.

That said, it's not the end of the road for Arnie or MJ's other creditors -- they can still sue the estate in court. But it's unclear if that's what Arnie and co. plan to do.

Dr. Arnold Klein provided serious drugs to Michael Jackson, which left the singer so out of it ... he couldn't even stand up straight ... this according to a new lawsuit obtained by TMZ.

In the lawsuit, filed by Klein's former assistant and confidant Jason Pfeiffer -- it is alleged "Throughout 2009, Michael was a frequent patient of Klein." The lawsuit continues, "Several times, Klein told Pfeiffer to help Michael down to the car because Michael was too drugged up and disoriented to stand on his own."

Pfeiffer says he voiced his concern for Michael's "safety" -- because he and Klein's nurses "were worried that Michael was being 'overmedicated' by Klein." Pfeiffer says Klein simply told him to "keep his mouth shut."

And there's more -- Pfeiffer claims Klein tried to sneak Michael prescription muscle relaxers in 2009 by writing a prescription in Pfeiffer's name.  Pfeiffer claims he refused to participate in the scheme.

Pfeiffer also claims in the suit ... sometime around October 2008, Klein was contacted by Michael Jackson, who told the doc he "needed 'to get out of a court appearance' and needed a doctor's note."

According to the suit, Klein told Michael he would take care of it and issued a note saying MJ was suffering from a Staph Infection ... based on a fabricated test.

Klein's treatment of MJ has been questioned in the past -- TMZ broke the story ... Klein injected Michael with 51 Demerol injections in the 3 months before Jackson died. Klein has always maintained that he treated Michael in accordance with the highest medical standards.

Pfeiffer claims he was wrongfully terminated by Klein -- and in the suit, filed Wednesday in Klein's ongoing bankruptcy case, Pfeiffer alleges that Klein forced him to help round up gay sex partners for Klein, including prostitutes and homeless people.

Pfeiffer also claims he would have to help "prepare" Klein for sexual encounters -- adding, "Klein required that Pfeiffer wash Klein's groin."

Pfeiffer -- who has stated in the past that he was Michael Jackson's gay lover -- says he suffers from severe emotional problems as a result of Klein's treatment -- and is suing for unspecified damages.

UPDATE: A lawyer for Klein tells TMZ, "Dr. Klein is one of the most esteemed and respected dermatologists in his profession in the country.  This counterclaim is totally unfounded, and frankly it's garbage.  The claims in Dr. Klein's lawsuit are very serious, and we're taking them all the way."

The man who claims he was Michael Jackson's gay lover says Dr. Arnie Klein is trying to sabotage his credibility because Klein is afraid the man will incriminate him during the Conrad Murray trial.



Jason Pfeiffer -- who once worked as Klein's office manager -- tells TMZ he's sticking to his story -- that he had a sexual relationship with the King of Pop -- despite Dr. Klein's recent Facebook post, calling MJ's gay affair a lie.

Jason insists, "The story is true. We had a relationship with sexual aspects, but I'm not going to make it into some grand love affair."

As we previously reported -- Klein himself had told TMZ that Michael Jackson had a gay relationship with Jason ... even calling Jason "the love of [Michael's] life."

But the good doc has since changed his story, writing on Facebook recently, "Allegations about ... Jason being Michael Jackson's lover are ridiculous. That story was made up ... "

Now, Jason claims Dr. Klein has a secret agenda to publicly discredit him -- in case Jason's possible testimony could paint Klein in an unflattering light.

Jason adds, "Klein was the one that pushed for me to release the story in the first place."

Dr. Arnold Klein -- the dermatologist who loomed large in Michael Jackson's life -- has now changed his story and says his good friend and office manager -- Jason Pfeiffer -- did NOT have an affair with Michael Jackson.



Klein had told TMZ ... Jackson was gay but that Jason's alleged relationship with the singer was the only gay relationship MJ ever had.  Klein told us Jason was "the love of [Michael's] life."

But now on his Facebook page, Klein says "Allegations about ... Jason being Michael Jackson's lover are ridiculous.  That story was made up ... "

Klein also scoffs at allegations he contributed to MJ's death, saying, "I made two interventions on Michael's Propofol Abuse myself ..."

Michael Jackson's friend and dermatologist Dr. Arnold Klein was forced to turn over medical records today from the final months of Michael's life ... TMZ has learned.



Dr. Klein and his attorney handed over the documents during a pretrial hearing in Dr. Conrad Murray's manslaughter case.

Murray's team wants the paperwork to determine exactly what drugs Klein used to treat MJ. As TMZ reported ... Klein's medical records show he injected Michael with Demerol 51 times in the three months before he died.

Last month, Dr. Klein asked the judge to quash the subpoena for his records. Fail.
 

Dr. Conrad Murray's lawyers just filed blistering legal docs, claiming Dr. Arnold Klein -- Michael Jackson's longtime doctor and friend -- addicted him to Demerol and another powerful narcotic.



In legal papers obtained by TMZ, Murray's legal team claims Klein fueled MJ's drug dependency by giving him scores of Demerol injections in the months prior to his death.  TMZ broke the story ... in the 3 months before Jackson died, Dr. Klein gave MJ 51 Demerol injections.

The docs claim, "Due to Mr. Klein's actions, Mr. Jackson became physiologically and psychologically dependent on Demerol." 

Murray's team wants Klein to produce all his medical records, claiming "Dr. Klein is a relevant and highly material witness to the defense."

Lawyers for some key witnesses in Dr. Conrad Murray's manslaughter trial over the death of Michael Jackson went to court today, trying to avoid giving up what could be critical evidence in the case.



Lawyers for Dr. Arnold Klein -- Jackson's longtime doc -- and AEG honcho Randy Phillips asked the judge to quash subpoenas issued by Dr. Murray, requiring them to produce information about MJ that the defense claims is relevant to his death.

Murray wants to find out exactly what drugs and treatment Klein gave MJ in the months before his death.  TMZ reported Klein injected Michael with Demerol 51 times in the 3 months that preceded his death.

As for Phillips, we've learned Murray's team wants to know what interactions AEG had with Michael -- in particular, AEG's expectations about Michael's rehearsal schedule and its involvement in selecting Dr. Murray as Michael's doc.

Lawyers for 5 other witnesses, including Tohme Tohme, Michael's former advisor, also tried to quash their subpoenas.

Michael Jackson was so worried he couldn't perform his London concerts in 2009 ... he worried out loud he would end up working behind the counter at McDonald's.


Karen Faye -- Michael's hairstylist for a quarter century -- was interviewed by LAPD detectives days after MJ died ... and TMZ has learned what she said to police.

Faye told cops, "He was scared to death because AEG was funding everything.  He said he would have to work at McDonalds if he didn't do these shows."

Faye also told investigators she believed Michael was "self-sabotaging" with drugs because he couldn't do all 50 shows.  Faye said she believed Michael needed psychological help because he was losing so much weight -- adding, "I thought he was under the influence of something."

Faye says Michael's assistant told her MJ was seeing Dr. Arnold Klein 3 to 4 times a week and was exhibiting signs of drug use.  Days before Michael died, when MJ seemed to be more lucid, she asked Michael's manager if he knew why Michael had taken a turn for the better.  His response, according to Faye -- "'Cause Klein is out of town."

Michael Jackson's doctor and longtime confidante,  Dr. Arnie Klein -- one of the most successful docs in Bev Hills -- has filed for bankruptcy ... TMZ has learned.



Klein -- who filed his petition in U.S. Bankruptcy Court in L.A. -- claims debts between $1 and $10 million.

Klein -- a dermatologist with an enormous celebrity clientele including Cher, Elizabeth Taylor and Dolly Parton  -- owes $80,000 to American Express, $127,000 to the IRS, nearly $2.6 million to City National Bank for a mortgage, $50,000 to one of his lawyers, $20,000 to the landlord of his office building, and $115,000 to Dr. David Rish, the doc who shares office space with Klein.

Klein, who also owes nearly a quarter of a million bucks to medical suppliers, filed for Chapter 11 last Thursday.