Bennell, 62, was taken to a hospital in Stevenage, north of London, on Friday night and has remained there since being found unconscious.
In a statement, Thames Valley Police said: "Officers attended an address in Knebworth Park, Stevenage, just before 11pm on Friday in connection with a 'fear for welfare incident.'
"A 62-year-old man was located and was taken to hospital in order to receive medical treatment, where he remains. At this stage of inquiries, it would be inappropriate to comment further."
In another statement, the East of England Ambulance Service added: "We received a call on Friday at 10.50pm to reports of an unconscious man on Knebworth Park in Stevenage, which we sent an ambulance crew to.
"The crew arrived within eight minutes to treat the man ... before taking him to Lister Hospital for further care."
Bennell was jailed for nine years in 1998 after admitting to sexually abusing children. One of his victims, former player Andy Woodward, broke his silence last week in an interview with the Guardian
In all, Bennell has been convicted three times for child sexual abuse -- including once in the US, where he also coached youth soccer camps.
He was sent to prison most recently in 2015 for a past sexual offense against a 12-year-old boy.
In a separate development Monday, police in Manchester confirmed they have launched an investigation into historical sexual abuse in the world of youth football.
"Following recent media coverage, Greater Manchester Police has received a number of calls from people reporting historic sexual abuse whilst they were in the youth football system," said Greater Manchester Police's Assistant Chief Constable Debbie Ford.
"We have now launched an investigation and our specially trained officers are supporting those who have come forward so far."
Greater Manchester Police are coordinating their investigation with Operation Hydrant, the national hub for child abuse investigations concerning persons of public prominence, Ford said.
"I would encourage anyone who was a victim of sexual or physical abuse to come forward and speak to us as soon as possible," she said.
Cheshire, Hampshire, Northumbria and the Metropolitan Police have also launched investigations of their own.