Nick Kyrgios has pulled out of his scheduled clash with Roger Federer at the BNP Paribas Open due to sickness.
The Australian, ranked 16th in the world, had beaten second seed Novak Djokovic in the round of 16 to set up a quarter-final against Federer but was unable to take to the court after a troubled night.
"Unfortunately I am unable to play today due to sickness," he wrote in a statement posted to his Twitter feed.
"At this stage we think it's food poisoning, and I'm praying it's nothing more.
"After a restless night of being sick I have nothing left and to play a great champion like Roger, I need to be at my best to have a chance.
"I don't take this decision lightly, these are the matches we train for but I'm in no fit state to take to the court. I'm sorry to the fans but I have to put my health first and I hope you understand.
"I want to wish Roger the best of luck for the rest of the tournament and thank everyone for their support so far here at the BNP Paribas Open. I will definitely be back. Thank you."
Federer tweeted his support to Kyrgios, stating: "hope you feel better."
Kyrgios' withdrawal spoiled the highly anticipated match with Federer, with neither player having dropped serve in the tournament.
"I was really looking forward to playing the match," Federer told fans waiting for the match on stadium court. "It's a pity."
Federer, who beat Rafael Nadal for the second straight time this year, 6-2 6-3 in the fourth round, will now await either American Jack Sock or Japan's Kei Nishikori in the semi-finals.
"I'm playing great tennis and I didn't expect it because I'm still on the comeback," said Federer, who won his record 18th Grand Slam title at the Australian Open in January after being sidelined by various injuries for much of 2016.
In the top half of the draw Swiss Stan Wawrinka will be a heavy favourite to advance to the final when he plays Spaniard Pablo Carrena Busta.