Black Sabbath is gearing up to play their final show ever this summer, and James Maynard Keenan is not convinced that Ozzy Osbourne will be physically able to perform. The TOOL singer, who helped induct Ozzy into the Rock and Roll Hall of Fame last fall, spoke about his concerns in a new interview.

Before touching on Ozzy's physical limitations, Keenan explained how his band TOOL got invited to perform at the Back to the Beginning extravaganza. “The conversation first came up when I was at the Rock & Roll Hall of Fame, hanging out with Wolfgang [Van Halen] and some of the guys, I think even Robert Trujillo,” he recalled. “We were on the travel over there, just going, ‘Okay, well, there’s a rumor about the Black Sabbath show.’ I was like, ‘Well, let’s do something.’ So I kinda had planned a song to do and all of a sudden I’m at home and I get the call, ‘Hey, Tool‘s been asked to do a song,’ and I’m like ‘Fuck.’ Now I have to call back Wolfgang and those guys and go, ‘I’m going to do it with Tool, sorry.’”

“That’s kinda how it came up, but I think for me, seeing Ozzy moving around at [the Rock Hall ceremony], the idea of him playing a show at all, if we’re being honest, the conversation about going to do the song was like, ‘We’ll have this conversation, but, ahh… I don’t know that this [concert] gonna happen,’" Keenan admitted. “And even now, I’m cautious about saying, ‘Yeah! All in, he’s gonna do it.’ Because man, I don’t know what kind of modern miracles we’ll come up with to get him on stage to do the songs, but this is gonna be a challenge for them. So, I’m honored to be a part of it, but I’m kinda preparing for the worst — but hoping for the best, as they say.”

Despite Keenan's reservations, Ozzy seems determined to perform—not just with Black Sabbath but as his final solo gig, too. The 76-year-old recently revealed that he's begun "heavy training" to get ready for the show.

Back To The Beginning and is to take place July 5 in Birmingham, UK. In addition to Black Sabbath, Ozzy Osbourne and TOOL, the all-day event will also feature sets from Metallica, Slayer, Pantera, Alice in Chains, and many other rock and metal icons.