Last month after an onstage breakdown during the iHeartRadio music festival in Las Vegas, Green Day frontman Billie Joe Armstrong checked into rehab for substance abuse. Now, Warner Bros. Records Chairman and producer Rob Cavallo is opening up about the potentially long road ahead for Armstrong and the band.

Commenting on the seriousness of Armstrong's condition, Cavallo told Rolling Stone that “his rehab is no joke” and that Armstrong is “under medical supervision for a while to get him clean.”

Green Day already canceled their headlining spot at the Voodoo Music and Arts Experience at the end of October (with Metallica filling in for them), but the band has additional tour dates kicking off in November.

Judging by Cavallo’s comments, more cancellations may be coming. “His doctors are still evaluating," Cavallo 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."

Bassist Mike Dirnt also recently spoke out about Armstrong’s current state of mind in an interview with BBC Radio 1 citing that the pressure of promoting three albums at one time weighed on all of them. “With hindsight 20/20, it was a tremendous undertaking,” Dirnt admitted. "Although we were having fun, we didn't take our nose out of the book for a long time. I think it catches up with you a little bit. We definitely just jumped off a moving train."

He also said that Armstrong’s breakdown wasn’t a complete shock. “There were signs of things hitting the fan," he said. "We hadn't slept in forever and Billie had definitely had the worst of it.” He continued, explaining, “He'd been going through his own struggles . . . We were there with him, but you can only handle things on your own . . . At the end of the day, when we got off the road, the most important thing was my friend's life."

Here’s wishing Armstrong a speedy recovery and a quick return to the stage.