A prison officer and an inmate from Mountjoy were hospitalised today in the second violent incident in the jail this week.
The pair were injured after officers tried to intervene in a row between two inmates.
Other prisoners refused to leave the area and the prison had to be locked down, although authorities said this was normal procedure at lunchtime.
Meanwhile, an inmate who was beaten about the head by another prisoner in a row over a TV remote control remains in serious condition.
A Prisons Service spokesman said: “One prisoner and one prison officer have been brought to the Mater Hospital as a precaution.
“It’s a minor incident. It’s not connected to the previous incident.”
Yesterday a 26-year-old prisoner was rushed to hospital with head injuries after being attacked the previous night by an inmate with a sock stuffed with batteries in a row over a TV remote control.
The injured man was brought to the Mater Hospital but later discharged himself and returned to the prison.
The next morning the Prison Service said he was difficult to wake and he was rushed back to the Mater.
The Prisons Service and Gardaí have launched two separate investigations into the incident.
Prison officers have frequently raised concerns about overcrowding in the Dublin prison, in which inmate Gary Douche was beaten and killed in August 2006.