James Grant, 24, said he was spear fishing Saturday near Colac Bay when he was attacked by a creature he believes to have been a sevengill shark, the BBC reported Tuesday.
"I had just gotten into the water, killed a fish and something latched onto my leg," Grant said.
"I thought it might have been one of my diving buddies, turned around ... big shark had latched on."
Grant told stuff.co.nz he used his diving knife to fight the shark.
"I sort of just fought the shark off. The shark got a few stabs. The knife wasn't long enough though," he said.
The junior doctor said he swam back to shore and stitched up his own wounds using a first aid kit.
Grant said his friends took him for a drink at a pub before continuing on to Southland Hospital.
"I am pretty grateful to have my leg still," he said.