A prison officer had part of his ear bitten off by an inmate during an attack at Nottingham Prison.
Police were called to HMP Nottingham just before 9.30am on Wednesday following reports of an assault on a prison officer.
"A prison officer had been assaulted and suffered a wound to his ear. He was taken to Nottingham's Queen's Medical Centre," a spokesperson for Nottinghamshire Police said.
"An investigation is under way."
It is the second incident to occur at a Nottinghamshire prison in less than a week after 120 inmates refused to return to their cells at HMP Ranby on Saturday.