The man said he was walking on West Addison Street near the CTA Red Line stop just after 12:45 a.m. when a male suspect walked up to him and started making threats, then hit him in the face.
The individual first allegedly claimed to be a security officer and then said he was a police officer.
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The suspect went north, and police tried to find him but were unsuccessful.
The victim declined medical treatment on the scene.
No one was in custody later Thursday morning. Area Three detectives are investigating.