Billie Joe Armstrong, Green Day Singer, Hospitalized
09/04/2012 AT 01:00 PM EDT
"We're beyond upset," said drummer Tre Cool in a video posted on the band's website. "We're as sad as you guys are. Billie is extremely upset about it."
Armstrong, 40, was "rushed to the hospital ... due to illness" on Saturday night, said bassist Mike Dirnt in the video.
The nature of the illness wasn't disclosed, but Dirnt said the "doctors didn't think it's a good idea" for Armstrong to play Sunday at a concert in Bologna.
He was discharged and later spotted at the airport in Los Angeles. Green Day was set to perform Thursday night at the MTV Video Music Awards.