According to Warner Bros. Records Chairman Rob Cavallo, frontman Billie Joe Armstrong's current rehab stay could lead to further Green Day show cancellations. 

“His rehab is no joke,” Cavallo told Rolling Stone. “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.”

“Before Christmas,” on Green Day's tour schedule includes 7 U.S. dates.  

Billie Joe entered rehab for substance abuse last month.