An internal police investigation was under way today after CCTV footage emerged which appeared to show officers repeatedly punching a stab victim.
Darren Grace, 31, claims he was assaulted by one female and two male officers as he was being treated for knife wounds in a Liverpool park last August.
The CCTV footage, published by the Liverpool Echo newspaper, appears to show a half-naked Mr Grace bleeding heavily and resisting the Merseyside Police officers' attempts to treat his wounds.
During the four-minute long recording, it appears he was punched several times to the head by a male police officer and later punched in the body by the female Pc and another male constable.
Merseyside Police said that CCTV images "can never show the whole story" and added its professional standards unit was investigating the matter.
Mr Grace, a joiner from Anfield, Liverpool, said he staggered into the city's Stanley Park disoriented after being stabbed at a friend's house in the early hours of Sunday August 1.
He was found by the officers slumped on the ground with bleeding head wounds.
Mr Grace was held at a police station for 11 hours following the alleged incident in the park, captured on CCTV operated by Liverpool Council's Citywatch scheme.
Charges brought against him of assaulting the police officers were later dropped by the Crown Prosecution Service (CPS).
Mr Grace said he had not made a formal complaint about the incident and he would not co-operate with Merseyside Police's internal investigation as he had "no confidence" in the force.
He is planning to sue the force and told the newspaper: "I remember waking up in the cell with my face covered in blood, my head throbbing.
"I could feel the cut where I'd been stabbed."
Superintendent Mike Shaw of Merseyside Police's Professional Standards Department said: "As a police force, we expect the highest standards from our officers. Where those standards are found to be breached, disciplinary action is taken.
"During the course of administering medical assistance to Mr Grace, he became violent towards the officers.
"In this case, I understand that members of the public will be concerned when watching this footage. However, I would like to stress that CCTV images can never show the whole story.
"The Professional Standards Department has been in contact with Mr Grace and his legal representatives and have been advised that there will be no complaint against police at this time, and that Mr Grace does not want to take part in any misconduct investigation.
"Nevertheless, in order to understand the full circumstances of the incident the Professional Standards Department has launched an investigation.
"This will include looking at the circumstances that initially led police to Mr Grace, the circumstances around his arrest and the circumstances, which led to the discontinuation by the CPS.
"It is important not to prejudge the outcome of the investigation. It would therefore be inappropriate to comment further at this time.
"This matter was voluntarily referred to the IPCC (Independent Police Complaints Commission) in recognition of the public concern it may generate, and the IPCC are happy that Merseyside Police carry out its own local investigation."
A spokesman for the IPCC added: "Having assessed all the available evidence, including the statements from officers, we are content at this stage for the matter to be investigated by Merseyside Police's Professional Standards Department without further IPCC involvement."