"Y'all ain't got to do that dog!" yells somebody as the man falls down. It's unclear when exactly the footage was taken.
"The Detroit Police Department was made aware, via social media, of an allegation of excessive force in Greektown. Internal Affairs is reviewing the circumstances surrounding this allegation," read a statement from police Monday morning. "DPD is committed to remaining transparent throughout this process and will provide updates to the community and our media partners as soon as practicable."
The man who was punched doesn't appear to react when officers try to lift him up. He eventually wakes up and begins shaking his hand at the police. Pedestrians then help him up as officers leave the scene.
Officers did not make any arrests during the scene.
The video, titled "Detroit pigs handing out the brain damage" has since circulated widely on the internet.
Greektown has been one of Detroit police's more active parts of the city since large crowds have congregated there in the wake of restaurant and business reopenings. Police Chief James White has previously asked for more resources to double the police presence in the area to stamp down on noise violations and brawls.
Another video of a Greektown knockout also circulated online in late July after a man was hit in the face.