Slipknot's guitarist Mick Thompson was stabbed in the back of his head by his brother Andrew on Wednesday, March 11.
The brothers were rushed to hospital in separate ambulances after a knife fight broke out at Mick's home in Clive, Iowa, the police confirmed to Billboard.
They both sustained serious, but not life-threatening, injuries.
It is thought the brothers were intoxicated when officers arrived, with Clive Police Chief Michael Venema telling the New York Daily News: "Neither individual was very cooperative. Our detectives will be following up as soon as their medical situation allows us."
Slipknot's lead singer Corey Taylor tweeted about the incident, saying: "In regards to the story about Mick, I'm doing the best I can to find out if he's alright. I'll get back to you later."
He later wrote: "Mick Update: from what I've heard he's okay. We're sending him all your thoughts. Thank you for that."
In regards to the story about Mick, I'm doing the best I can to find out if he's alright. I'll get back to you later.
— 'Mad Beans' Hooper (@CoreyTaylorRock) March 11, 2015Mick Update: from what I've heard he's okay. We're sendig him all your thoughts. Thank you for that.
— 'Mad Beans' Hooper (@CoreyTaylorRock) March 11, 2015