The death of New Zealand All Blacks star Jonah Lomu, aged 40, was unexpected and the cause is unknown.
But he has a long history of kidney problems.
The Independent reported he was on a waiting list for a kidney transplant and has been undergoing regular dialysis since 2011 when a kidney from a 2004 transplant failed.
That happened on the same night he starred in the opening ceremony of the 2011 World Cup in New Zealand.
He was rushed to hospital and didn't leave hospital for two weeks.
His doctor John Mayhew said it was a close run thing.
"For a while there, Jonah was an extremely sick man," Dr Mayhew said.
"There was a distinct possibility he could have died as a result of serious renal failure."
Lomu wrote in his book Jonah: My Story: "My bloodstream was septic and the doctors were starting to think the worst: that my kidney had failed and my body was in total meltdown."
He was diagnosed with nephrotic syndrome in 1995.
This kidney condition is usually caused by one of the diseases that damage the kidneys' filtering system, allowing the protein albumin to be filtered out into the urine. When the protein level in the blood drops, liquid seeps out of the smallest blood vessels, causing swelling all over the body.
Normally, a person loses less than 150mg of protein in the urine in a 24-hour period, but a person with nephrotic syndrome can lose more than 25 times that amount, according to the Victorian government's better health website.
Treatment includes medications and dietary changes.
- by Catherine Armitage, smh.com.au