Green Day frontman Billie Joe Armstrong has been released from an Italian hospital after being felled by an undisclosed illness over the weekend.

The band was forced to cancel a headlining appearance at the I-Day Festival in Bologna, Italy, on Sunday, September 2, after Armstrong was rushed to the Hospital Maggiore overnight. While there are still no explanations behind the illness, WENN reports that local sources infer Armstrong was suffering from gastric problems.

Green Day was quick to get in front of the situation, with band members Tres Cool and Mike Dirnt issuing a video apology to their fans in Bologna.

“The doctors don’t think it’s a good idea for him to play today,” Dirnt explained. “This sucks, we really, really, were looking forward to playing in Bologna. It’s a highlight of our tour.”

The WENN report also states that overzealous Green Day fans caused something of a ruckus at the hospital in attempts to see Armstrong.

Green Day’s next scheduled appearance is at the iHeartRadio Music Festival in Las Vegas on September 21.

–Scott T. Sterling, CBS Local