Manson was supposed to undergo surgery on Thursday but doctors determined he was too weak and the procedure too risky.
US mass murderer Charles Manson, who was rushed to hospital earlier this week, is suffering from intestinal bleeding but is too weak to undergo surgery, media reports said on Friday.
The 82-year-old, who is serving nine life sentences for the 1969 grisly killing of seven people, including pregnant actress Sharon Tate, was reportedly transported from California's Corcoran state prison to a hospital in Bakersfield on Sunday.
The celebrity gossip website TMZ said Manson was supposed to undergo surgery on Thursday but doctors determined he was too weak and the procedure too risky.
TMZ said doctors wanted to perform surgery shortly after he was rushed to hospital but he refused.
Manson finally agreed to go under the knife on Thursday but his condition was too weak, TMZ said.
"Manson remains in hospital and doctors are trying to figure out their next move," it added.
Manson headed an apocalyptic cult that went on a killing spree in 1969 in upscale, mostly white neighborhoods of Los Angeles. The group hoped to blame the crimes on African Americans and spark what Manson termed a "Helter Skelter" race war.
He was sentenced to death in 1969 along with four of his "Manson Family" disciples for having led the killing of seven people -- including director Roman Polanski's wife Sharon Tate, who was eight months pregnant -- but their sentences were later commuted to life in prison.
Manson, who was not actually present but ordered the bloody rampage, has been denied parole 12 times and is not eligible to apply again until 2027.
A prison official told AFP that during his more than 40 years behind bars, the cult leader had accumulated well over 100 rules violations, including for assault, possession of a weapon, threatening staff and possessing a cellphone.
"He cannot be described as a model inmate," said Terry Thornton, a spokeswoman for the California Department of Corrections and Rehabilitation.
Thornton said she could not comment on Manson's health condition because of privacy laws.