Carfrae nursing arm fracture at Ironman

A fractured arm has left Australian great Mirinda Carfrae hoping for some magic at the Hawaiian Ironman triathlon.

The three-time winner suffered the injury last month in an innocuous fall during a training run.

Carfrae's record at Kona means she will still be among the favourites this Sunday (AEST) but will need a lot to go her way.

The swim is already Carfrae's big weakness and it is where the injury will affect her most.

"Me of all people can't afford to really be swimming any slower but I will probably - I'd say definitely - be slower than normal out of the water," she said.

"But ... I feel that I will be able to get through the swim okay and I will be able to put together a bike and run, and you never know.

"Magical things have happened on that island before and I'm hopeful that I can create some magic again.

Carfrae last won Hawaii in 2014 and was fifth last year, after becoming a mum for the first time.

Swiss great Daniela Ryf is on a five-year winning streak and is the woman to beat again in the 3.8km swim, 180km cycle and 42.2km run Ironman-distance world championships.

Sarah Crowley, third two years ago, is the other top Australian hope among the women.

A year after finishing in the top 10 for the first time, former top rower and pro cyclist Cameron Wurf is the Australian to watch in the men's race.

Wurf sparked plenty of debate when he won Ironman Italy only three weeks out from Kona, clocking a blistering sub-eight hour finish.