The 63-year-old guitarist has been diagnosed with lymphoma and, following a statement from the band asking fans to send "positive vibes" to him, has thanked fans for their well wishes.
He said: "I just want to say how overwhelmed I am with all your messages of support, thank you so much. Well it's not what I wanted for Christmas, that's for sure, but now I can't wait for the test results to come in and get going with the treatment."
The rest of the group - which has recently reunited its original line up, which sees Tony joined by Bill Ward, Geezer Butler and Ozzy Osbourne - have made the decision to move from working in Los Angeles to the UK, so they can all work on their first album together in 33 years.
He added: "It's really good that the guys are coming over so that we can continue working on the album as things are going great in the studio. Not much else to say at this time, so thanks again."
The band are set to headline Download Festival, which starts on June 10.