The actor, 32, injured his hand and ended up in the emergency room on Wednesday after punching a mirror on the set of his new film Nightcrawler, but he smiled as he posed with Maria Bello on the red carpet at ArcLight Hollywood.
A source close to the star tells PEOPLE that the actor received stitches to his left hand but returned to the set in L.A. hours after the accident.
Gyllenhaal lost 20 lb. for his role as a crime-scene reporter in the drama, and the accident happened during an "emotionally charged" scene, when his character was looking into a mirror.
"Jake flipped out," a second source tells PEOPLE. "He punched the mirror in anger and broke it, cutting himself so bad he had to be taken to the hospital."