Zoo spokeswoman Laurie Skene said the employee was receiving medical treatment but wouldn't say how badly injured the person was or the type of animal involved.
However, those details were provided by Lisa Glover of Occupational Health and Safety, which is investigating the incident.
Skene says the zookeeper was working outside a cage and the animal was inside.
The zoo has had recurring problems with staff and its lowland gorilla exhibit, including leaving doors open in the apes' enclosure.
Earlier this month the zoo announced that two employees were disciplined over a door incident a few weeks ago that allowed six gorillas to escape into a kitchen at the facility.
A similar incident happened with the kitchen door in March and the employee involved was fired.