It happened during a race on Sunday afternoon.
Officials say harness racing driver Anthony Coletta was thrown into the air after a collision involving four horses and their drivers.
Coletta then hit the ground and was trampled.
He was rushed to the Hospital of the University of Pennsylvania for surgery. He remained in critical condition Monday. However, on Monday evening, Action News learned that Coletta was breathing on his own.
Anthony DeFrancesco, a friend of the victim, watched as the crash unfolded on the track.
"A horse had taken a bad step around the last turn and fell, and Anthony was behind him," said DeFrancesco.
Action News has learned Coletta was driving a horse named Straight Up Tequila. The horse that went down first was Rocknmy Jeans, driven by Marcus Miller.
"Coletta is a young driver with a lot of talent," DeFrancesco told Action News. "He's somebody for the future of this sport. It's odd, because normally he races a horse out front and this time he had one in the back and it kind of worked against him."
Caesar's Entertainment, which owns Harrah's, released the following statement Sunday night:
Earlier this evening there was an accident involving four horses and their drivers at Harrah's Philadelphia. One of the drivers is being treated for his injuries, and while complete information of the extent is not available at this time, our first concern is for the well being of the driver involved, and we send our thoughts and prayers to his family and friends.