The garda was responding to a report of a number of males acting aggressively in the city centre at the time.
Armed Gardaí also responded to the scene on Cruses Street around 11.30pm, Saturday night.
A source said the injured Garda was allegedly pushed and knocked over by a male youth, before she fell and hit her head off the ground.
A 17-year old male was arrested on suspicion of assaulting the Garda.
The Garda was being treated at University Hospital Limerick for minor injuries, according to Gardaí.
“A male youth, aged 17 years, was arrested for assaulting a Garda member and was taken to Henry Street Garda Station where he remains detained currently under the provisions of Section 4 of the Criminal Justice Act. The Garda member attended University Hospital Limerick with minor injuries.,” a Garda spokesman said.
“Investigations are continuing.”
Meanwhile, a man in his 20s was arrested by Gardaí in connection with an alleged public order offence arising out of the same incident.
“Gardaí, including members of the Armed Support Unit, attended the scene of an incident on Cruises Street, Limerick, that occurred at approximately 11.30pm. A man in his 20s was arrested for breaches of the Public Order Act and was detained at Henry Street Garda Station,” the spokesman said.