A trauma surgeon says it is "pretty rare" to reattach legs, despite reports that surgeons made an attempt for surfer Kai McKenzie.
"It has to be a clean, fresh amputation," Professor Ian Harris said.
Kai, who is being treated at John Hunter Hospital, was attacked in the surf at North Shore Beach in Port Macquarie on Tuesday last week.
The 23-year-old fought off the three-metre great white shark and caught a wave to shore, before being flown to hospital.
He confirmed on social media that he lost the leg, which washed ashore soon after the attack.
Locals put the leg on ice for transport to the hospital.
Professor Harris, a Sydney-based orthopaedic surgeon, said "we have to make this decision all the time with incomplete amputations".
"You get someone who's been run over by a train or something like that and their leg is virtually detached, with just a few tendons holding it on.
"If somebody comes in for something like this [a severed leg], we'll have a discussion with the plastic surgeon who will do the nerves and the vascular surgeon who will do the blood vessels.
"We decide whether it's worth doing or whether we'll give it a go."
Professor Harris, of UNSW Sydney, said when legs were badly damaged, there wasn't much point in trying to reattach them.
"We have shiny new ones [prosthetics] that work better, so we tend to not put bad legs back on."
He said severed limbs could not be reattached if they weren't taken to hospital quickly.
"Anything longer than six hours, then the decision is made for you because it won't live, it will be a dead limb, unless it's being kept on ice."
He said fingers were easier to reattach because they "don't have muscles in them".
"Skin can live for a long time. You can put skin in the fridge for a week and stick it back on someone later.
"Muscles and nerves die.
"If you're putting something back on that has to move again, then the muscles have to be alive."
Meanwhile, a GoFundMe set up for Kai surpassed $175,000 on Wednesday, with a target of $250,000.
"Kai is currently in John Hunter Hospital where he has had surgery and is in a stable condition," Lauren Mac said on the GoFundMe.
"As you can imagine, the upcoming medical expenses for his recovery and rehabilitation is something no one would ever be prepared for.
"The funds raised will go in assisting Kai in every aspect of his recovery."
Lauren is a neighbour of the McKenzies.
"They are a local family with hearts of gold that would never expect or ask anything of anybody, so let's give back and show them that they have the community's support in this."
Kai and his parents Jane and Grant had "expressed their appreciation for all the donations and are extremely grateful for all the support".
"Kai has an absolute fighting spirit and has outlined that he intends on returning to the water in no time."
