Around noon local time on Sunday, security guards on patrol noticed that the middle-aged victim had climbed a long mesh fence and entered the enclosure of a lion, a lioness and two cubs.
His motivation has yet to be determined.
“The intruder was attacked by a lion and injured him,” the state forestry commission said on Sunday.
Officials are probing the incident.
There were no animals left during the incident and the enclosure is safe, the statement said.
Lions are a top attraction at the Accra Zoo, where reinforced mesh fences allow visitors to see predators up close.