Malcolm Young is taking a break from AC/DC to focus on his health, the band said.
The announcement saying the 61-year-old guitarist is in "ill health" was posted on the band's Facebook. No details were provided.
"Malcolm would like to thank the group's die-hard legions of fans worldwide for their never-ending love and support," the statement said.
AC/DC includes vocalist Brian Johnson, drummer Phil Rudd, bassist Cliff Williams and guitarist Angus Young, Malcolm Young's brother.
The Rock and Roll Hall of Famers said in the statement they "will continue to make music." AC/DC's last studio album was 2008's "Black Ice." They released a live disc in 2012.
Young co-founded the Australian classic rock band. He has performed with AC/DC for 40 years.
Mark Gable, a friend and musical contemporary of Young, said he doubted the guitarist would ever record again.
"It's not just that he is unwell, it's that it is quite serious," Gable, frontman of the Australian band The Choirboys, told Australian Broadcasting Corp. radio.
"He will probably not be able to record," Gable added.
Sydney-based music company Alberts, which launched AC/DC's international career and manages the band's music catalogue, did not respond to a request for comment.