Singer, songwriter and guitarist Bo Diddley is in intensive care following a stroke during a concert in the US.
Bo Diddley is regarded as one of the pioneers of rock 'n' roll
The 78-year-old appeared disorientated during a gig in Iowa. The musician has a history of hypertension and diabetes.
Tests indicated that the stroke affected the left side of his brain, impairing his speech and speech recognition, a spokeswoman said.
Diddley first topped the R&B charts with Bo Diddley in 1955. He was given a lifetime achievement Grammy in 1998.
The spokeswoman said there were no further details on his condition, or how long he would be in hospital in Omaha, Nebraska.
He was due to play 11 dates across the UK at the beginning of June.
Diddley, with his black glasses and low-slung, rectangular guitar, has become an icon in the music industry with hits including Who Do You Love, Before You Accuse Me, Mona and I'm a Man.
He was inducted into the Rock and Roll Hall of Fame in 1987.
With his trademark "hambone" rhythm, he has been a lasting influence on rock 'n' roll and rhythm and blues.
"I play the guitar like I'm playin' the drums," he has said. His style was adopted by Buddy Holly, Bruce Springsteen and The Who, among others.