Atlanta police told television station that the shooting occurred about 5:30 a.m. today. WSB reported that one of the three men left the scene and returned with a gun. Police believe the man and security guard exchanged gunfire and the man was hit.
The man died after being taken to an Atlanta hospital.
Police have recovered two weapons from the scene.
Police Maj. Keith Meadows told WSB that police do not expect to file charges against the security guard. Police were also investigating whether the nightclub was operating legally.