Investigators say the victim just left work and was walking down the 600 block of Leithgow Street at around 5:20 p.m. with proceeds from the popular, cash-only cheesesteak establishment.
The unarmed thief approached the manager, knocked him to the ground, and took off with the loot, valued at approximately $30,000.
"You don't expect something like this to happen especially on a Sunday afternoon," the manager of Sweettooth candy store, a few doors down from Jim's Steaks, told Action News.
He believes he may have seen the suspect across the street on a park bench shortly before the crime.
Detectives taped off the area around the bench and searched for possible clues.
"While I think I may have seen him, I couldn't describe him," he said.
Investigators canvassed the area looking for surveillance video.
They suspect it may be an inside job or possibly committed by a previous employee of the company who would know the manager's routine.
"If you did the math, one and one doesn't equal three. If that was the case, I'd clean house if it was my establishment," the Sweettooth manager said.
Police don't have a description of the suspect to release to the public.
The Jim's Steaks manager was uninjured during the robbery.