The band posted a statement online which read: "We are truly sorry to inform our fans and friends that we must postpone our upcoming tour of Australia and New Zealand.
"As most of you probably know, our brother James has been struggling with addiction on and off for many years. He has now, unfortunately, had to re-enter a treatment program to work on his recovery again."
Now, Slipknot – who were set to be supporting Metallica on their Australian and New Zealand dates – have issued a statement to fans addressing the cancellations.
Via a statement posted to their Facebook page, the band told fans: "To our Australian and New Zealand fans and family, we only recently heard the news about the tour being postponed, and we are working as quickly as possible to determine next steps.
"We will let everyone know as soon as we are able. Of course, our thoughts are with James and Metallica. We wish them nothing but the best.
"We hope to see you all very soon."
At the time of writing, Metallica's other future plans are still on schedule, including a charity concert in March 2020 to raise money for the band's All Within My Hands Foundation, a series of South American dates in April, and the Global Goal Live show in September.