Jeffs, 55, had been fasting for the past three days and became so weak that doctors at the Texas prison where he is serving a life sentence induced a coma, according to the source.
The leader of a radical polygamist sect of Mormonism known as the Fundamentalist Church of Jesus Christ of the Latter Day Saints (FLDS), Jeffs is scheduled to go on trial a second time in October to face charges of first-degree bigamy. Conviction would be punishable by up to 99 years or life in prison and up to a $10,000 fine.
Jeffs was moved last Tuesday to a solitary cell at the Powledge Unit in Palestine, Texas, because of the large amount of media coverage surrounding his case, prison officials said.
Polygamous Sect Leader Warren Jeffs in Critical Condition
He is now being treated at the East Texas Medical Facility in Tyler, Texas, the nearest major medical center to the Powledge Unit, Michelle Lyons, spokesperson for the Texas Department of Criminal Justice , told ABC News.
Lyons said Jeffs is in "critical but stable condition," but added, "I cannot confirm that he is in a coma."
Prison officials are prohibited from releasing the specific medical conditions for which Jeffs is currently receiving treatment due to the federal health privacy policies.
"He did indicate to staff that he was fasting, but he is currently being treated for other medical ailments and conditions," she said of Jeffs.
A Texas jury found Jeffs guilty Aug. 4 of forcing two teenage girls into "spiritual marriage," and fathering a child with one of them when she was 15.
He was sentenced to life in prison with no chance of parole for 45 years. Jeffs must serve at least 35 years of a life sentence on one of the child-sex charges, and at least 10 years on the other.
Warren Jeffs Reported to Be in Coma
The Powledge Unit is one of the smaller facilities in the Texas prison system, housing just under 1,000 inmates.
Jeffs was to be in his cell for 22 hours a day, allowed out only for recreation and a shower.
The prison is located in southeast Texas, about a six-hour drive from the Yearning for Zion Ranch in remote Eldorado, Texas that serves as the headquarters for Jeffs' followers.
During his weeks-long trial, prosecutors presented DNA evidence showing Jeffs fathered a child with a 15-year-old girl who lived at a Texas compound raided by police in 2008 where Jeffs ran the FLDS sect. Prosecutors also played audio recordings of a sexual encounter between Jeffs and a 12-year-old girl.
Jeffs accused police of discriminating against the West Texas compound because his followers looked and acted differently than mainstream society. Officials denied it.
"A sexual assault of a 12-year-old and 15-year-old girl has nothing whatsoever to do with religious persecution," Texas Attorney General Greg Abbott said today. "If anybody of any religious background comes to Texas and sexually assaults young girls, they are going to be investigated and prosecuted regardless of what their religious background is."
Texas state prosecutors wrapped up their case against Jeffs by using his own words against him: a disturbing August 2006 audio recording of what Jeffs' called a "heavenly comfort" training session with three of his so-called "spiritual wives."
Sexual contact with his wives, Jeffs believes, revives him spiritually and brings the girls closer to God.
Texas Ranger Nick Hanna testified the recording was found when Jeffs was arrested during a traffic stop in Nevada. Another copy of the tape was found at the Yearning for Zion ranch when it was raided in 2008.
Jeffs' sect broke off from the mainstream Mormon Church 72 years ago. His 10,000 followers across North America consider him a prophet who serves as God's spokesman on Earth.