A second former All Black is in hospital with kidney issues - and has spoken out to urge rugby legend Jonah Lomu to step back from his boxing commitments.

Joeli Vidiri told the Herald on Sunday from Middlemore Hospital that he was admitted last Sunday for a check-up but was not sure when he would be allowed home.

Vidiri, who played two tests for the All Blacks, was forced to retire in 2001 after being diagnosed with kidney disease.

"Life is not that long, (Jonah) has to be happy with his life and do what he loves but I want to say to him to take it easy and go step-by-step, day-by-day," Vidiri said.

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He said Lomu should think twice before taking part in a boxing charity event.

Last week, the Herald on Sunday broke the news that Lomu was in Auckland City Hospital's renal and liver ward.

His wife and manager Nadene Lomu declined to comment on his condition.

New Zealand Woman's Weekly confirmed this week it had signed a deal with the family.

In the interview it was revealed the kidney Lomu received in 2004 is failing him, and it's likely he will need another transplant.

Lomu had been training with professional boxer David Tua for December's Fight For Life where he was expected to take on Warriors wing Manu Vatuvei.