Machine Head guitarist Phil Demmel collapsed on stage during the band's set in Nissan Pavilion in Bristow, Virginia last night (August 17).
Demmel had been complaining of feeling light headed throughout the show, and passed out during the second-to-last song due to severe dehydration.
"That was a scary moment for all of us," said MH drummer Dave McClain. "Seeing your friend collapse like that is something that nobody wants to experience."
However Demmel is expected to make a full recovery and will rejoin his bandmates for the final date of the Rockstar Mayhem tour on Tuesday, August 19 at the Darien Lake Performing Arts Center, New York.
"He's doing much better now," adds McClain. "and is taking it easy on the bus."
Machine Head will tour the UK in the autumn with Slipknot and Children Of Bodom.