Former All Black Joeli Vidiri has told the UK Daily Telegraph that both he and Lomu both took creatine while they were playing with the Blues in the 1990s.
Vidiri, 42, believes the muscle-building supplement may have contributed to the kidney disease which ultimately led to Lomu's death late last year and caused his own kidney condition.
Both Vidiri and Lomu were diagnosed with nephrotic syndrome, a rare kidney disease that affects only three in 100,000 of the population.
The Telegraph quoted medical experts as saying taking creatine would have impacted on Lomu's disease.
But former All Black doctor John Mayhew told the Telegraph that Lomu never took the supplement.
The Blues doctor at the time Lomu was playing for the Super Rugby franchise, Graham Paterson, told the New Zealand Herald this morning that no players were encouraged to take creatine during his tenure.
However, he said he could not speak for what players might have been doing away from training.
"Creatine was widely used in New Zealand rugby," he said.
Vidiri was diagnosed with the disease 15 years ago and finally underwent a transplant last May.
Lomu had a transplant in 2004, but it failed seven years later, and he died of a sudden heart attack last November at the age of 40. His death was almost certainly linked to his kidney problems.
Vidiri told the Telegraph Lomu took the substance even after being diagnosed with nephrotic syndrome in late 1995.
"We were in our prime and enjoying ourselves, and you ask, 'why us?'" Vidiri told Telegraph Sport. "It's a question we can't answer for sure. Lots of people have been telling me about creatine and it does make you wonder.
"I would be happy if somebody came through with a study to help with that - and to help the young people who are taking it now. We need to know what are the side effects of taking it. I would love to know that because we can advise the young people about the right way to go."
Vidiri added: "We used to be given a really big container of it [creatine] every few months. Instructions were written on the back and we would take the container away with us.
"We used to mix it with water and it would puff you up. I can't remember how much we would take anymore. We took it before we trained and after too. Jonah would take it too, though maybe not as much, because he was already on the drugs for his kidney condition.
"We took it from 1997 onwards. We used to have a corner in the dressing room where we'd sit together."
Vidiri said there was huge pressure on the players to perform at the Blues.
"The supplements were part of that because you wanted to get stronger. The game was getting tougher and faster. You wanted something to help you improve in your rugby career. I stopped taking creatine when we started to get worried about what it was doing to us. As soon as there were rumours about it, I stopped."
Dr John Mayhew, who was Lomu's personal GP, denies that the legendary wing took creatine.
"We knew he had a renal impairment for most of his career, so he definitely wasn't taking it. It is not a banned substance, but as a rule of thumb I advise anyone with kidney problems not to take it."
Professor Phillip Kalra, consultant nephrologist at Salford's Royal Hospital, told Telegraph Sport that significant creatine use would have worsened Lomu's kidney condition.
He said there was evidence that "massive people are more predisposed to nephrotic syndrome" and research has shown that Polynesians have a higher predisposition towards the condition than average.
