The `Cheers (Drink to That)` hitmaker - who is currently on a world tour - has been hooked up to a drip at a Swedish medical institution and has been forced to cancel a performance in the city of Malmo in the south of the country after being stricken with the flu.
Tweeting a picture of her arm with a tube coming out of it, Rihanna wrote: "Sorry Malmo!"
In a statement, the 23-year-old singer added she was "really disappointed" she could not perform.
According to TMZ.com, she said: "I am sorry to everyone who was coming out to my show in Malmo. I was so excited to perform for you all. It would have been a great time. So much better than being sick with the flu, ugh. I`m really disappointed I couldn`t be there."
A representative for concert promoter Live Nation added she was "not in condition to conduct the concert".
Rihanna is not the only star to be forced to cancel a planned concert recently - George Michael had to pull out of a gig at London`s Royal Albert Hall after he was diagnosed with a viral infection, leaving him with a high temperature.