The Rock and Roll Hall of Fame member told the BBC in a recent interview the diagnosis comes after he began having difficulty remembering his songs and the names of people he's worked with.
A spokeswoman did not immediately reply to a message left by the Associated Press.
The soul singer has cut a wide path through the music business as a performer and songwriter in his 50-year career and recently launched another act with "The Bravest Man in the Universe," the Damon Albarn-produced comeback album that recently made several best-of lists.
Alzheimer's is a degenerative brain disease characterized by memory loss. It's the latest health problem for the 68-year-old singer, who's also been fighting cancer and other maladies.
