Officers say they hope he can assist them with their inquiries into the assault in Poundland, in Sauchiehall Street, Glasgow, on May 30.
The incident took place at around 5.15pm that day as many people were shopping after work, and extensive inquiries are currently under way.
Detectives directly appealed for the man, thought to be in his 40s, to contact them as it is believed he may have witnessed the incident or have information that could help with the investigation. Police said he was wearing a white baseball cap, glasses, navy blue jacket, light-coloured body warmer and a blue T-shirt.
He was also wearing dark denim jeans with the bottoms turned up, and he was carrying a khaki backpack.
Police hope the distinctive description will help to quickly identify the man.
Inspector Kenny Darroch, who is leading the inquiry into the incident, appealed for the witness to come forward.
He also urged anyone who can help identify the suspect to come forward. He said: "I would appeal to anyone who was in Poundland on Sauchiehall Street around the time of the incident to contact officers."