He revealed on his Instagram Story: “Towards the end of the show on Wednesday I started feeling ill and I’ve been in bed with the flu ever since.
“I’ve been doing everything I can to be able to sing tonight, but I’m leaving the doctor now and I’m devastated that it’s just not possible.
“I’m sorry this news is coming so close to show time, but it was my sincerest hope to be able to play for you tonight.
“I know several of you have planned trips to LA to see the show, and it means the absolute world to me.”
In June this year, the As It Was hitmaker helped an Italian fan come out as gay at his Wembley Stadium concert.
The fan, named Matteo, was holding a sign that read: “From Ono to Wembley: Help me come out.” during Harry’s two-night stint at the London venue and the former One Direction star declared Matteo “officially gay my boy” as he raised a Pride flag above his head.
He said: “Congratulations Matteo, you are a free man.”