Lingering complications from Dave Mustaine's back surgery have forced Megadeth to cancel a scheduled appearance this month on Motorhead's Motorboat, a heavy metal-themed at-sea concert event. They'll be replaced by Metal Allegiance, an all-star group that features Megadeth's Dave Ellefson and Chris Broderick.

According to a released statement, "Upon his doctor’s strict recommendations, Dave Mustaine has canceled all performances for the next eight weeks. With rest and treatment, he is expected to recover and resume performing soon."

Cruising aboard the Carnival Ecstasy, Motorhead's Motorboat leaves from Miami on Sept. 22, and then continues to Key West and Cozumel through Sept. 26. The headlining Motorhead will be joined by Anthrax, Testament, Down, Kill Devil Hill, Zakk Wylde, Danko Jones and others. Metal Allegiance also includes Philip Anselmo, as well as members of Anthrax, Kill Devil Hill and the Winery Dogs.

Mustaine underwent cervical spine surgery in 2011, citing a condition called stenosis that he said was caused by years of headbanging. That's the same procedure that helped the NFL's Peyton Manning return to the field with Denver a couple of years ago.