In a statement today promoters said the Australian soft-rock star had been hospitalised with a severe infection after having minor surgery two weeks ago.
This would affect the Dunedin Forsyth Barr Stadium show this Saturday in which he was meant to open for The Eagles.
His shows in Auckland and Wellington shows will be postponed.
At the tail end of his national Tūrangaewaewae Tour, Williams and band were on a scheduled night off this Saturday but have taken up the opportunity to open for one of the "most important bands in the world", promoters said.
"The Eagles have the biggest selling album of all time. Being a part of this show is going to be magic and surreal," Williams said.