The singer - who kicked off her new Diamonds World Tour on Friday night - fell ill immediately after her debut show and pulled out of her performance in Baltimore on Tuesday night despite taking three days off to get better.
The singer is said to be extremely disappointed that she has only been able to perform one show to date.
The 25-year-old admitted she was gutted after announcing her first cancellation in Boston on Sunday and wrote on Twitter: "BOSTON this is the hardest thing for me to deal with! I feel like we've been waiting on this day forever, and I'm hurt that I let you down
"I hate disappointing people that never ever let me down!! I'm so embarrassed about this! Thank you for your prayers and well wishes!#DWT"
Live Nation previously said the singer was under doctor's orders to rest, saying: "Unfortunately, following her sold out concert on Friday, Rihanna has contracted laryngitis and per doctor's instruction is unable to perform this evening."
Both of her shows in Baltimore and Boston will be rescheduled.
A source previously claimed that Rihanna couldn't wait to get out on tour and took it easy in rehearsals so she could save her energy for her fans.
The insider said: "She's good, excited to kick off this [tour] and do it big. She's already hyped up and doing some light rehearsals but other than that, she's taking it easy. Saving all the energy for the show."
The singer is still currently scheduled to take to the stage in Philadelphia on Thursday.
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