The group reunited in 2012 for a series of gigs and released a new album, titled 13, last year (13).
But, despite ongoing talk of a reunion extension well into 2015 and another studio album, Iommi fears the group's upcoming London gig in July (14) will be the last time the veteran rockers hit the stage together.
He tells Metal Hammer magazine, "It could be the last ever Sabbath show. I don't want it to be, but there's nothing really planned touring-wise after that show, so for all we know that could be it really. To be honest, I don't want to be touring to this extent too much longer, because it makes me feel so bad."
Iommi completed treatment for lymphoma earlier this year and is waiting to hear his latest prognosis from doctors, adding, "I'm at a stage now where I have no support, which means I have to see whether the cancer is coming back or if it's still there or what. I just don't know. It's a bit of a worry. After we finish this tour I'll go in and have scan, so we'll see what that shows up."