The actor was discharged after he received stitches Wednesday morning, then returned to work later in the day, the report said.
"Jake flipped out," a set insider told People.com. "His character was looking into a mirror during the scene and punched the mirror in anger and broke it, cutting himself so bad he had to be taken to a hospital."
A source close to Gyllenhaal told People.com the incident was nothing more than the result of an intense scene at the end of an 18-hour day.
"The scene was emotionally charged and his character was talking into a mirror and he got so into it, he banged his hands against the mirror and it broke and cut him," the source said. "It was all the scene and not because he was mad about anything else."