Heavyweight Daniel Dubois' world title defence against Joseph Parker on Saturday is off after the champion fell ill two days before the fight.
The Briton was medically evaluated in Saudi Arabia and missed Thursday's news conference, before being withdrawn later in the evening.
Dubois, 27, was scheduled to make a second defence of his IBF title. There is no information on the nature of his illness.
New Zealand's Parker, 33, will instead fight Congolese Martin Bakole, who has been drafted in as a late replacement.
"If he is ill, I hope he gets better soon and I'm looking forward to Saturday and having a great show," Parker said before learning of the replacement.
Parker later told Sky Sports, external: "He did a sensible thing. If you're sick, don't fight.
"There's no point going out there and fighting your heart out and you're not in the right physical shape. Go out there and fight when you're at peak, top shape, top condition, and put on your best performance. Put your best foot forward and the one that everyone will remember."
Dubois has won 22 pro fights with two defeats. He won the 'interim' IBF title against Filip Hrgovic and was elevated to world champion when Oleksandr Usyk vacated the belt.
The Londoner made a first defence of his belt by stopping Anthony Joshua in five rounds at Wembley Stadium in September.
Parker has a record of 35 wins and three defeats. He held the WBO heavyweight title between 2015 and 2017.
The highly rated 33-year-old Bakole, who is based in Scotland, has lost once in 22 bouts with 16 knockouts.
The contest is the chief support to the undisputed light-heavyweight fight between champion Artur Beterbiev and Dmitry Bivol.
Also on the card, Briton Hamzah Sheeraz challenges Carlos Adames for the WBC middleweight title.
