Blake, who married Winehouse in Miami, Florida, in 2007, was found choking on his own vomit in bed by Sarah Aspin, the mother of his 15-month-old son Jack.
She then hospitalised him in Yorkshire, England, reported Sun online.
Doctors put him on a life support machine after he allegedly swallowed his tongue and suffered multi-organ failure.
"The doctors don't know the prognosis and put him in a coma to help him. I'm praying he'll survive but I'm having to prepare myself that he may never wake up," Aspin said.
"He has never really been a drinker, but when he got home with this friend, he was slurring his words and staggering. I thought he was on something. I was very angry because he had been doing so well," Aspin added.
Blake, whose pop star ex-wife Winehouse passed away almost exactly a year ago, has battled a heroin addiction. He is said to have introduced Winehouse to crack cocaine and heroin.