The 67-year-old, who is suffering from a degenerative nerve disease similar to Parkinson's disease, is being treated at the Baptist Hospital in Nashville, Tennessee.

"He was readmitted on Sunday after spending several days here last week," hospital spokeswoman Jessica Etz said. "He is not critical, his life is not in danger."

Cash performing in 1973

The star's agent Lou Robbins said he hoped Cash would be allowed home after the weekend.

However, family friend Scott Tyne is quoted in a newspaper report as saying: "We're all praying for the best but expect the worst."

In November 1998 Cash announced he had Shy-Drager syndrome, a progressive disease that attacks the nervous system.

Later that month he was admitted to hospital with pneumonia and nearly died.

However, in April this year he was the surprise performer at his own all-star tribute in New York - taking the stage for the first time since he was diagnosed. Sheryl Crow and Willie Nelson were among the others stars on the bill.

The singer, known as the 'Man in Black' told the audience: "I haven't been on stage in 19 months. It feels good, feels good, feels good."

His simple, raw sound has won nine Grammys and he is the only musician to be inducted into the Songwriters' Hall of Fame, the Country Music Hall of Fame and the Rock and Roll Hall of Fame.

In a career spanning five decades, he has sold more than 50 million records, His string of hits includes Folsom Prison Blues, Ring Of Fire and A Boy Named Sue.