A prison officer was taken to hospital after reportedly being stabbed in the head by an inmate at a young offenders' institution.
The member of staff was transferred to hospital after the incident at HMYOI Wetherby on Thursday, and discharged later that day.
The prisoner believed to be responsible was stripped of his privileges and placed in the segregation unit.
A Prison Service spokesman said: "An officer at Wetherby prison was taken to hospital on Thursday 10 March following an incident involving a prisoner. The police are investigating. Violence against our hard-working staff will not be tolerated."