Tony Azzopardi, 56, said that he wants to help the police work out what happened to the singer in her last hours but claims he is terrified of reprisals from the dealer he arranged for her to buy drugs from.
"I want Amy's family to know the truth about what happened," he told the Daily Mirror. "I want to help them out -- but I'm worried about my safety."
Azzopardi claims Winehouse approached him outside a pub in Camden, north London, on July 22 at around 11:30pm local time and asked him to help her buy drugs. He said that they took a cab together to nearby West Hampstead, where he called the dealer -- described as a local "Mr. Big" -- to come and meet them.
Winehouse paid the dealer $2,000 for half an ounce of crack and the same amount of heroin, Azzopardi claims, before she headed home in the early hours of the next day.
He added that Winehouse complained to him that her ex-husband, Blake Fielder-Civil, had been calling her from prison and "hassling" her.
The soul singer was found dead by her bodyguard at around 4:00pm local time July 23.
Despite Azzopardi's claims, police said they found no evidence of drugs or drug paraphernalia in her home, and the Winehouse family said his account did not match up with the singer's movements.
Her father, Mitch Winehouse, 60, told mourners at the star's funeral last week that she quit drinking after being clean of drugs for several years. The family believes she died of a seizure or heart attack because her body could not handle going "cold turkey" from alcohol.
An autopsy proved inconclusive, and it could be several weeks before the results of toxicology tests may establish the cause of her death.
Tim Bittlestone, of law firm Leslie Franks, told the newspaper, "Myself and Azzopardi attended Kentish Town police station. We will speak to them again on Monday."
Police refused to comment.
Mitch Winehouse, who said last week that he wanted to set up a foundation in his daughter's memory, was due to meet lawmakers Keith Vaz and James
Brokenshire on Monday afternoon to discuss setting up a drug rehabilitation center for young people struggling with substance abuse.
The singer's multiple Grammy award-winning album, "Back to Black," topped the UK charts Sunday night. Her debut album, "Frank," appeared at No. 5, and five of her singles were in the top 40.