David Cassidy's condition is so serious that doctors have summoned his immediate family to the hospital to be with him

A source told TMZ: "There's really no issue anymore for a transplant. It's futile."

The website previously reported that the 'Partridge Family' star needs a liver transplant, and is also suffering from kidney failure.

A source told the publication: "It's looking grim."

The site has also claimed that doctors have told David's family - including daughter and actress Katie Cassidy, 30, whom he has with former partner Sherry William, and son Beau, 26, whom he has with ex-wife Sue Shifrin - "they need to prepare for the worst," given the star's deteriorating condition.

This comes as the latest health scare for David, who revealed earlier this year he was battling with dementia, which is a persistent disorder of the mental processes caused by brain disease and marked by memory disorders and personality changes.

The 'Daydreamer' singer took to his website to share a touching message where he thanked his fans for supporting him throughout his career, and for sending "messages of concern and care" during his struggle with the illness.

In March, he wrote: "To the many thousands of people who have supported me over the last 5 decades I send my love. I thank you all sincerely for the support and care you have shown me recently and in the past.

"I am enjoying some time at home, appreciating the warmth and contemplating what I will be doing next. I wanted to let you all know that I am not retired, I do want to play again. I just won't tour. I also want to go back into the studio to record 'Songs My Father Taught Me'. I will keep in contact with you and let you know what I am doing.

"Thank you for the many letters and messages of concern and care. I have my good days and very occasionally a bad day. I am doing everything my doctors advise in terms of diet and pills.

"Happy Trails, DC (sic)"