Sgt. Daniel Urban was handcuffing the suspect in the front of his police cruiser, parked on Saddle River Road, when the vehicle was rear ended just after 1:30 a.m. Friday.
The force of the collision send the cruiser lurching forward at the sergeant and his handcuffed suspect.
Urban threw the suspect out of the way of his vehicle, but was struck himself.
The 25-year police veteran sustained head injuries and cuts to his legs.
He was taken to Hackensack University Medical Center, where he was treated and released.
The suspect was also treated for non-life threatening injuries at the hospital.
Charges against him are pending.
The driver was not charged, and authorities believe the crash was an accident.