Robert Whittaker out of fight against Kelvin Gastelum at UFC 234

FILE – In this June 10, 2018, file photo, Robert Whittaker reacts after his middleweight mixed martial arts title bout against Yoel Romero at UFC 225 in Chicago. Whittaker defends his UFC middleweight title against Kelvin Gastelum in the main event of UFC 234 in Melbourne, Australia, on Sunday. (AP Photo/Jim Young, File)

MELBOURNE, Australia — Australia’s UFC middleweight champion Robert Whittaker withdrew from his championship defense against Kelvin Gastelum on Sunday at UFC 234 because of an abdominal injury and subsequent emergency surgery.

UFC president Dana White says the 29-year-old Whittaker, who has a record of 20-4, became ill Saturday night and complained of pain in his abdomen before being diagnosed at a hospital with a hernia.

In a later statement, UFC said Whittaker had undergone emergency surgery due to a “severe abdominal injury.”

The highly anticipated No. 1 contender match between rising New Zealand star Israel Adesanya (15-0) and Brazilian veteran Anderson Silva (34-8) will now serve as the main event on the Rod Laver Arena card.

Elevated on the card was the lightweight bout between American Lando Vannata and Brazilian Marcos Mariano.

Tickets for the 15,000-seat arena sold out in eight minutes. UFC has offered full refunds due to the cancellation of the main bout.

It marks the second time Whittaker has been forced to withdraw from a scheduled title fight in Australia. Injuries kept him from fighting Luke Rockhold at UFC 221 in Perth last year.

Earlier this week, White had said the winners of the Whittaker-Gastelum and Adesanya-Silva fights would meet later this year.