The department says the officer and his partner were conducting surveillance on the corner of 63rd and Oxford streets around 6:00 p.m.
Two men were in the middle of a drug deal when the officers went for the takedown.
They got the suspected drug dealer, but the buyer made a run for it.
"The driver of the car takes off at a high rate of speed, striking a couple of parked cars and then he strikes the police officer in the leg. That officer discharges one time attempting to stop the vehicle and the vehicles flees the scene," Philadelphia Police Lt. John Walker said.
Police marked off the area where the officer's shell casing landed on the street.
Zorina Briggs who was on her way to her parents' house for the holiday says the suspect almost ran her off the road during his getaway.
"He almost kind of crashed into my car, he kind of shook up my kid and I thought the guy was drunk because he was going really fast," Briggs said.
Moments later, she saw the plainclothes officer in the middle of the street.
He was transported to the Hospital of the University of Pennsylvania with injuries to his leg.
"Officers are out here doing their jobs and unfortunately this person decides to take an action with a car that could have potentially killed that officer and that officer had to take action," Walker said.
The suspect fled in a black Nissan and remains on the loose.