Zoo director John Gibbons said today the woman, in her 20s, was picking agapanthus inside a barricade next to the enclosure when she was bitten by a young male lion.
She lost the top of her middle finger in the attack, which occurred last Thursday.
It is the second attack by a big cat at the zoo in a month, after a nine-year-old boy on a school excursion was badly scratched by a Persian leopard.
But zoo officials said such attacks were very rare, and it was disappointing that zoo patrons sometimes disregarded safety fences.
“We do ask all our patrons to stay behind the safety barriers here at the zoo and she explained at the time that she was picking some flowers,” Mr Gibbons told ABC radio today.
“It’s not a wise thing to do to climb over a safety barrier and collect a flower here at the zoo.”
Mr Gibbons said the lion was believed to have eaten the finger, but staff were advised against searching for it.
The woman alerted staff to the attack about 5pm (AEDT).
She was treated at the scene before being taken to Royal Melbourne Hospital.
Melbourne Zoo will now install electric fences inside the lion enclosure to prevent similar attacks.
“It’s very rare, we get over a million people here at the zoo… and these sorts of occurrences are very rare indeed,” said Mr Gibbons.
Last month, a nine-year-old school boy on a zoo excursion was badly scratched by a Persian leopard.
The boy had left his group, climbed a barrier and leaned on the lion’s enclosure.
An ABC talkback caller recalled a similar incident about three years ago when a friend was bitten by a lion when she was at the zoo attending a function.
“The lion was resting near the fence and he (the friend) climbed over and was scratching the lion’s back and the lioness came up and bit his finger off,” the caller told the ABC.
Mr Gibbons said he was aware of that incident, which occurred late at night after the patron moved away from a function and into an off-limits area.