We haven't heard from Green Day singer Billie Joe Armstrong since the singer's onstage blow-up last month at the iHeartRadio music festival in Las Vegas preceded his trip to a rehab facility to deal with unspecified substance issues.

Bassist Mike Dirnt said earlier this month that the band's hard work on their album trilogy caught up with them a bit and that, "at the end of the day when we got off the road the most important thing was my friend's life."

Now, the band's long-time producer and Warner Bros. Records chairman Rob Cavallo has spoken out about the status of Armstrong's rehab and how it might affect the band's touring and promotional plans later for the rest of the year.

"His rehab is no joke," Cavallo told Rolling Stone magazine. "He's under medical supervision for a while to get him clean." So far, Armstrong's rehab has forced Green Day to cancel an October 27 appearance at the Voodoo Music and Arts Experience in New Orleans (Metallica has stepped in to replace their Bay Area brethren). Their tour is supposed to kick off on November 26 with a show at Seattle's Paramount Theatre and keep them on the road through February, but Cavallo said there's no guarantee they'll make those dates either.

"His doctors are still evaluating," he said. "All I can say is I don't know if we'll see him before or after Christmas. It's basically undetermined when he'll be back." The band still plan to release the second part of their album trilogy, ĄDos!, on November 13. A spokesperson for the band could not be reached for comment on the band's future plans.

This story appears courtesy of MTV News.