Black Sabbath had concerns over whether Brad Wilk was the right man to replace Bill Ward, it has emerged.
Bassist Geezer Butler told Faster Louder that there were times that it seemed the Rage Against The Machine man might not be the perfect pick to replace Bill Ward.
Butler said: "We literally had two weeks to work with him before we recorded the songs. The first week we were going, 'This guy's just not working out,' and we were panicking.
"We went into the studio and recorded the first three songs with him - and that was probably where Rick [Rubin] really worked out the most. He had the definite idea of what the drummer should do, so he was communicating with Brad, and he's worked with Brad before.
"It just all fell into place. He did a great job in the end."
Sabbath release new album 13 on Monday.