UPDATE: Armstrong has been released from the hospital after being admitted Monday night, according to TMZ. The musician was unable to speak when cameras documented him leaving the hospital -- he reportedly lost his voice.
PREVIOUSLY: Green Day was forced to cancel a concert at the I-Day Festival in Bologna, Italy, on Sept. 2 after the band's frontman was rushed to the hospital, NBC News reported.
Details about what is ailing singer Billie Joe Armstrong were not released. However, Green Day bassist Mike Dirnt and drummer Tre Cool posted a video on YouTube to apologize to fans and to explain that Armstrong's doctors advised him not to perform this weekend.
SEE VIDEO ABOVE.
According to The Daily Mail, Green Day's new album trilogy, "Uno!", "Dos!" and "Tre!" will be released in three stages over the next few months. The band also plans to put out two documentaries featuring vintage concert footage and a behind-the-scenes look at the trilogy's recording process.