By Lindsay Kimble
Updated May 04, 2016 at 03:26 PM EDT
Credit: Richard E. Aaron/Redferns

Prince died just one day before he was expected to meet with a doctor to discuss treatment for an addiction to prescription painkillers, an attorney with knowledge of the singer’s death investigation told the Minneapolis Star Tribune.

Dr. Howard Kornfeld, the medical director of California’s Recovery Without Walls outpatient addiction clinic, was planning to fly to see Prince in Minneapolis on April 22 after the star’s representatives said he was “dealing with a grave medical emergency,” the doctor’s attorney William Mauzy told the Tribune.

Prince was found unresponsive in his Paisley Park estate on April 21, and declared dead on the scene. His cause of death has yet to be revealed, but is being investigated as a possible drug overdose, a law enforcement official told The Associated Press last week. Investigators are also reportedly looking into whether a doctor was prescribing the singer drugs before his death.

Sources previously told PEOPLE that the singer had a history of using the prescription painkiller Percocet.

Howard’s son, Andrew Kornfeld, flew to Minnesota the night of Prince’s death, intending to explain how treatment would work and devise a plan. “…The doctor was planning on a lifesaving mission,” Mauzy told the Tribune on behalf of the Kornfeld family.

Andrew arrived at Paisley Park at 9:30 a.m. on April 21, and was one of three people present when Prince’s body was found in an elevator. Mauzy told theTribune that Andrew was the one who called 911, which is why he didn’t know Paisley Park’s address.

Mauzy told the Tribune that Howard wanted Prince to relocate to California for long-term care under his supervision. He noted that Prince’s representatives called Kornfeld because of his reputation as an addiction research expert.

Andrew has turned over the small amount of medication Suboxone — a drug that helps cure opioid cravings — that he brought with him to Paisley Park. He had intended to give it to Prince upon his arrival, according to Mauzy.

An autopsy of Prince’s body was conducted on April 22, and the medical examiner found “no obvious signs of trauma.” Full toxicology reports may take weeks to complete, however.

In the meantime, the Drug Enforcement Administration is also helping the county sheriff in Prince’s death investigation.