A police spokesperson said the assault took place at 6.30pm Thursday at the Fresh Choice supermarket on Edgeware Rd.
Police received a report of disorderly behaviour. A man had allegedly hit a supermarket employee.
The manager of the Edgeware Fresh Choice, who did not want to be named, said the assault happened there. He had no other information to give.
Ambulance services were not required.
Police were making inquiries to locate the suspect.