An inmate at Corradino prisons was hospitalised early on Sunday after harming himself.
The case happened at about 8am in Division One.
The man, Keith Gravina, 42, is in critical condition, sources said. He was imprisoned a few weeks ago after being convicted of assaulting a woman while she slept at home. He faces separate charges of assaulting another woman and drug possession.
The prisons agency the inmate was quickly assisted by trained staff. He was seen by a psychologist two days ago and had shown no intention of harming himself.
A magisterial inquiry is underway.