The Malmsbury Youth Justice Centre was placed into rotating lockdown last Friday following the assault of two staff members by inmates on Thursday.
The latest incident is the fourth assault on staff over the past fortnight, and resulted in serious head and facial injuries.
WorkSafe and union officials met with staff on site on Friday and conducted a unit by unit inspection.
The union highlighted that reduced staffing levels was putting workers at risk. Union representatives are now working with the Department of Justice to ensure the centre operates with a full complement of staff.
It is understood at least two inmates connected to the assaults have been transferred to the Parkville Youth Justice Centre.
