New York  - Michael Jackson, 50, is reportedly suffering from a potentially fatal lung disease, US news reports said.

The King of Pop suffers from Alpha-1 antitrypsin deficiency, a rare genetic illness, an unconfirmed report said, adding that he may have to undergo a lung transplant.

"He's had it for years, but it's gotten worse," Ian Halperin, author of a book on Jackson, told In Touch magazine. "He needs a lung transplant but may be too weak to go through with it... [But] it's the [gastrointestinal] bleeding that is the most problematic part. It could kill him."

The singer, known for his hits Thriller or Bad, can barely speak and is almost blind on his left eye.

Jackson is rarely seen in public. A few weeks ago, he was photographed in Los Angeles, wearing a Zorro-style mask.

His brother Jermaine Jackson told television channel FOX News: "He is not well." (dpa)