The British singer and talent show judge, 33, had been due to sing at a festival in the Hungarian city of Debrecen on Saturday but was advised by medical professionals that she needed time to recover from an unspecified illness.
She told her Instagram followers in a story post: "Please forgive this unexpected turn of events but sadly I will not be able to perform at Campus Fesztival tonight.
British-born Rita Ora married New Zealand filmmaker Taika Waititi in 2021. (EPA PHOTO)
"Having spent the night in hospital in Budapest, I must rest thoroughly and follow doctors' orders.
"I am so sorry to my fans who are going to be there today and I'm truly thankful for your understanding."
Next month, Ora is scheduled to perform at the Lovestream Festival in Slovakia, the City Celebration 2024 in Romania and Manchester Pride.
She released her third studio album You & I, in 2023 as a follow-up to 2018's Phoenix and her 2012 debut Ora.
The I Will Never Let You Down singer is also a judge on The Masked Singer on both sides of the Atlantic and a coach on The Voice Australia.
She started dating the Oscar-winning filmmaker Taika Waititi in 2021 when they were both working in Australia, and the pair married the following year in Los Angeles.
Ora, also known for her acting, recently appeared in the musical fantasy film Descendants: The Rise Of Red, where she plays the tyrannical Queen of Hearts.
She has also appeared in Kung Fu Panda: The Dragon Knight, and in the erotic Fifty Shades series alongside Jamie Dornan and Dakota Johnson.
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