The steps outside the main entrance to the church, as well as much of the nearby Windsor Road, were cordoned off after the incident.
The man was treated in the Emergency Department and was later discharged.
The police – including armed officers – were at the scene for much of Sunday morning.
In a statement issued on Sunday evening, the States police said they wanted to trace a man and a woman who may have witnessed the assault.
They also released new information about the disturbance, saying one man ran off towards New Street while the other was left lying on the pavement by the church’s northernmost car park.
Anyone with information about the incident, which happened between 5 am and 5.30 am, is being asked to phone the States police on 612612.