The incident occurred at about 10:25 p.m. at a Taco Bell in the first block of East Chicago Avenue.
Police said a 47-year-old man who was a former worker at the restaurant walked in and demanded his paycheck. The 27-year-old manager told him that he could not provide his check at the moment and police said the suspect then jumped over the counter and began attacking the manager with a box cutter.
The manager was cut in the back of the head and the arm, police said. He was transported to the hospital in fair condition.
The suspect fled the scene and is not in custody. Area Three detectives are investigating.