The wound, which lies between the actor's elbow and shoulder, was incurred while staging a high-energy dance number, reports the Daily Mail.
"I was singing the Queen song 'Bohemian Rhapsody', dancers were flying all over the place and a girl’s heel got stuck into me and drew blood," he said.
"I think at that very moment of contact I reached my highest notes."
Groff, who plays show-off Jesse St.James, added: "I was lucky, though. Some had bruises, there was a broken limb or two, others drew blood. It was like a scene from Gladiator."