All Black great Jonah Lomu's transplanted kidney has failed, leaving him needing intensive dialysis and another new kidney to survive.
Lomu has had to spend time in hospital and is now 30kg lighter than when he launched the Rugby World Cup in September.
Kidney disease forced a transplant eight years ago but in October that organ - donated by his friend and radio host Grant Kereama - stopped working.
Lomu, 36, revealed in this week's New Zealand Woman's Weekly that he was ill again and the transplanted kidney had not responded to treatment.
"We were hoping to see some improvement but nothing has made any difference, so the next step is to try to find a donor."
Lomu's immune system is so low that an ankle injury got infected so badly that he couldn't walk and wound up in hospital.
He told the magazine he was having dialysis for seven hours, three nights a week. But he was focusing on spending as much time as possible with his family.
Kidney Health New Zealand education manager Carmel Gregan-Ford said finding a suitable donor for a second transplant was difficult because the recipient had more antibodies than before their first transplant. However, she knew people who had had two or three transplants, including one woman whose third transplant was still working after 15 years.
She said about 130 people received transplanted kidneys last year.
Nadene Lomu, mother to Lomu's sons Brayley, 3, and Dhyreille, 16 months, said in the magazine she was struggling to cope. "When trial after trial is smacked in your face, it can be hard. I'm beginning to wonder what else can go wrong."