During Gaga's performance of Judas, a male backup dancer smashed Mother Monster over the head with a metal set piece as she was trying to pretend-fire a prop machine gun.
Gaga briefly paused the moment the set piece hit her upside the head, only to jump back into the rest of the song as she scuttled off stage.
The singer was only gone for a few moments before coming out and telling the audience, I want to apologize. I did hit my head and I think I may have a concussion. But don't you worry, I will finish this show. She went on to play a 16-song set.
Tara Savelo, Gaga's makeup artist, later tweeted about the head hit.
Gaga has a concussion but she is going to be okay. She wants u to know she loves u. I'm taking care of her. Can't believe she finished the show, she wrote.
The singer herself hasn't said anything about the incident since the show, with her Twitter feed going quiet.