The break-in happened around 1:30 a.m. Saturday at a home on Pea Pond Road in North Bellmore.
Investigators say the 36-year-old victim returned home and heard a noise coming from upstairs, eventually finding the suspect in a bedroom.
Police say the suspect told the victim he was a cop and took out a shield.
A struggle ensued, but the suspect broke free and ran away.
The victim suffered a broken arm in the confrontation and he needed stitches to his head and face.
The subject is described as a male, approximately 5-foot-8 and 160 pounds, last seen wearing a black jacket and a brown ski cap.
Detectives request anyone with information about the above crime to call Nassau County Crime Stoppers at 1-800-244-TIPS. All callers will remain anonymous.