Health bosses say Tavistock Minor Injuries Unit (MIU) will stay closed until November due to staffing shortages.
Last week the hospital warned patients about the planned closure, before it was confirmed on Wednesday morning.
The unit is usually open from 9am to 10pm seven days a week, but the hospital say it has 'become harder to keep the unit open due to our small team being affected by unplanned absence.'
The MIUs at The Cumberland Centre in Plymouth and in Kingsbridge will remain open.
Tavistock MIU sees an average of around 23 patients a day. Patients who would normally use Tavistock should use The Cumberland Centre or call NHS 111.
For more information, contact University Hospitals Plymouth NHS Trust's Patient Advice and Liaison Service on 01752 439884.