“Malcolm is suffering from dementia and the family thanks you for respecting their privacy,” his spokesperson confirmed in a statement to People.
The 61-year-old musician, originally born in Scotland, had already announced he would not be returning to the group after taking a long break earlier this year due to an unspecified illness.
AC/DC are set to release new album, Rock Or Bust, in December.
They start a new world tour in 2015.
Malcolm’s nephew, Stevie Young, who played rhythm guitar on the new LP, will play in his place.
Last week, the Sydney Morning Herald reported that Young had been moved into a nursing home to receive full time care in Sydney.
“If you were in the room with [Young] and walked out, then came back in one minute later, he wouldn't remember who you are. He has a complete loss of short-term memory,” a family friend apparently told the publication.
Scottish-born brothers Malcolm and Angus Young (the school uniform-wearing lead guitarist) formed AC/DC in 1973.
Most famed for the track “Back In Black” (1980), they have sold over 200million albums worldwide.Reuse content