Prison officials said the state prison in Tecumseh is on a modified lockdown after a second staff member was assaulted by an inmate this week.
State Patrol Spokeswoman Deb Collins said a caseworker was severely beaten by an inmate on Sunday and is suffering from broken bones, head injuries and a broken ankle.
Prison officials said that on Wednesday a second staff member was assaulted by another inmate. The staff member was treated at a local hospital and released.
Prison officials said they suspect inmate Leo Thomas of the Sunday beating. Collins said he is serving a 13-to-19 year sentence for robbery and assault charges.
Authorities identified the inmate suspected of the second beating as Thomas McBride, who is serving a life sentence for murder.
The prison said it is not releasing the names of the staff members. Both inmates have been placed in segregation.
Prison officials said the modified lockdown status will continue while the assaults are being investigated.