Merseyside police have confirmed a 27 year old man is being questioned following an incident at Broadgreen Hospital in Liverpool in June.
Police say there had been an allegation of assault against a patient by a health care assistant the previous day.
It's reported that incident involved a 79 year old female patient, the subject of an ongoing police investigation, who has now been transferred to a nursing home in the city.
A 27-year-old man has voluntarily attended a police station in relation to this matter and enquiries are ongoing.
This follows the arrest of a male health care assistant on suspicion of attempted murder after what's described as a 'serious incident' at the hospital in July.
Merseyside Police said officers were contacted by staff at Broadgreen Hospital on 22 July and an investigation is under way.
A 31-year-old man has been arrested and released on conditional bail.
A hospital spokesman said there is "no suggestion" patients or their loved ones should be concerned over safety and they had taken 'appropriate action'.