Taulupe Faletau is hoping to raise £50,000 for his cousin’s life-saving treatment.
The Bath Rugby and Wales star has set up a Gofundme page to help Amanaki, who suffered kidney failure in 2015 and is undergoing dialysis in New Zealand.
However, because the 21-year-old is from Tonga – where Taulupe was born – and not a New Zealand resident, it costs £3,100 (NZ$6,000) per month.
Amanaki is in debt to the health board and has been advised to pay off some of that debt to help his application to become a permanent New Zealand resident.
As a permanent resident the essential treatment would be free and he could be on the waiting list for a kidney transplant.
Faletau has put £5,000 to the cause, while clubmates Anthony Watson and Charlie Ewels have also contributed.
Saracens and England prop Mako Vunipola, who grew-up in Pontypool with Taulupe, has also donated to the total now approaching £14,000.
On the fundraising page, Taulupe explained that Tonga does not have a dialysis centre because it would take up a fifth of the Pacific island’s health budget and only one per cent of the 108,000 people who live there need dialysis.
He wrote: “While this is understandable, it is heartbreaking for the 1% who desperately need treatment.
“Without dialysis a kidney failure patient would likely die within a few weeks.
“Being in NZ and receiving dialysis is his (Amanaki’s) only hope of survival and without it, [he] wouldn’t be here today.
“As a family and a community we have raised some funds to help with this over the last three years, but most of his treatment has been at the mercy of the health board and he has now become in debt with them.
“To say the least it has been a very hard, sometimes helpless three years for Amanaki and his mother Lia who have been separated from the rest of their family who are still in Tonga, trying to deal with mounting debt and worrying about the status of their application.
“If their application is denied and Amanaki is deported to Tonga it would be less than a matter of weeks before his illness took his life.”
To donate, visit Faletau’s page.