An ex-doctor of former All Blacks star Jonah Lomu says the champion probably died from a blood clot on his lung.

John Mayhew, who treated Lomu regularly, told BBC Radio the 40-year-old most likely died instantaneously from the clot, which probably formed during a long-haul flight back to his New Zealand home last week.

The rugby champion suffered from a rare kidney disease for two decades and was forced into retirement in 2002, but Dr Mayhew said he was in good health right before his sudden death last week.

• Jonah Lomu dies at 40
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“We think the most likely cause was a clot on the lung which can be a complication of long distance travel,” Dr Mayhew said.

“Jonah was at greater risk of that happening because of his renal condition.”

Lomu received an unsuccessful kidney transplant in 2004 and was on dialysis until the time of his death.

He had been in England working in a commercial capacity at the Rugby World Cup, before spending some time in Dubai with his family.

Lomu Tweeted a picture of himself enjoying dinner with a local friend in Dubai only the day before his death, at age 40.

Tributes flowed for the man who inspired many young rugby stars, including current All Blacks champion Sonny Bill Williams.

“When we saw him on the world stage, doing what he was doing and accomplishing what he was accomplishing, that gave us a sense of pride and the feeling that we could do that, that any islander could do that kind of thing, the star told Fairfax.

Lomu is survived by his wife Nadene and their sons Brayley, six, and Dhyreille, five.