Mick Thomson, who plays lead guitar for Slipknot, has been stabbed by his brother during a drunken fight.
Police in his home city of Des Moines in the US state of Iowa say they were called to his house early on Wednesday morning.
Chief of Police Michael G Venema said his officers were called to reports of two brothers fighting in a front yard.
When they arrived they found Thomson with a stab wound to the back of his head.
Mick and his brother Andrew were taken to separate hospitals with non life-threatening injuries.
Speaking to Newsbeat, patrol officer Danny Anderson said both men had now been released. Neither was arrested and the police investigation continues.
According to local reports, the band's manager says Mick's injuries won't stop Slipknot performing.
Ahead of headlining the Friday night of this year's Download festival they start touring next month when they play the Fort Rock festival in south Florida.
Tweeting about the incident, Slipknot's lead singer Corey Taylor thanked fans for their thoughts.
Last year the band released their first album in six years, titled 5: The Gray Chapter.