An investigation has begun into claims that police officers assaulted a 21-year-old man while he lay handcuffed on the ground in Nottingham.
The man was treated in hospital for serious chest and facial injuries after being arrested on Sandringham Road, Sneinton, at about 0100 GMT on 25 July.
Nottinghamshire Police has referred the incident to the Independent Police Complaints Commission (IPCC).
The IPCC has appealed for witnesses to the arrest.
IPCC Commissioner Amerdeep Somal, said: "When instances of serious injury happen following contact with the police they inevitably give cause for concern to the public.
"In this instance a young man has suffered serious injury after alleging that he was assaulted while lying on the floor handcuffed.
"I would appeal to anyone who witnessed the arrest to contact our investigators."