Dr. Conrad Murray's criminal defense team has been dealt a crushing blow when the judge presiding over his involuntary manslaughter trial, ruled that Michael Jackson's dermatologist and long time friend, Dr. Arnold Klein won't be allowed to testify.

Dr. Murray wasn't in court for the pre-trial hearing on Monday in Los Angeles.

Judge Michael Pastor agreed with the Los Angeles County District Attorney's Office -- which opposed the defense's attempt to call Dr. Klein as a witness in the trial.