Chris Munce will not ride at the Magic Millions meeting at the Gold Coast.
Munce will begin seven weeks of radiation therapy on January 7, five days before the Millions meeting, after being diagnosed earlier this month with throat cancer.
He will miss the ride on Sizzling in the $1 million Magic Millions Guineas (1400m) as well as Sir Luminar in the $2 million Magic Millions Classic (1200m).
Sizzling's trainer Kelso Wood has booked champion jockey Craig Williams to ride Sizzling in the Guineas but Munce will still be aboard the colt at his next start in the Vo Rogue Plate (1350m) at Doomben on Saturday week.
"One of the hardest things I had to do today was ring Kelso Wood and connections to let them know I would not be able to ride Sizzling in the Guineas," Munce said on his blog.
"I'm devastated to miss the ride. He's my favourite horse and the connections have been great supporters and I wish them well with the colt."
Michael Nolan said Munce would ride Sir Luminar in Saturday week's B J McLachlan Stakes at Doomben but hasn't finalised a rider for the Millions.
Munce's last day of riding before he starts treatment will be at the Goldmarket meeting at the Gold Coast on January 1.
He has set himself the goal of returning to riding at the winter carnival and reuniting with Sizzling who will be set for the Stradbroke Handicap at Eagle Farm in June after his Millions campaign.
"I can assure you all I will be back better than ever," he said.
Munce has won the Magic Millions Classic three times - aboard Sunblazer (1989), Excellerator (2001) and Dance Hero (2004).