The "Love Lies" hitmaker has been supporting Ariana on the North American leg of her "Sweetener World Tour" since its launch in March, but she had to skip the most recent gig after suffering an undisclosed ailment.
Hours before showtime, Normani took to social media to alert fans of the change in plans.
"Following doctor's orders, Normani regrettably will not be able to perform at tonight's Sweetener tour stop in Pittsburgh," read a statement posted on her Twitter and Instagram accounts.
However, the former Fifth Harmony star is hoping to be back in action by Friday night (June 14), when the trek makes a four-night stop in New York City, starting with two dates at Brooklyn's Barclays Center, before transferring to the fabled Madison Square Garden in Manhattan.
"We apologise to the fans in Pittsburgh," the notice continued. "We hope to see you soon and look forward to returning to the stage in NYC this weekend."
Although Normani was absent from Wednesday's line-up, fellow tour openers, pop duo Social House, performed as scheduled in its hometown.
The Pittsburgh gig proved to be an emotional one for Grande, who was visibly overcome with emotion throughout the show as it marked her return to her late ex-boyfriend Mac Miller's native city.
The rapper died from a drug overdose in September, 2018, aged 26.