Jesy Nelson has tested positive for COVID-19.
The 30-year-old pop star has been forced to pull out of Hits Radio Live in Birmingham after being diagnosed with the virus.
Jesy - who has been preparing for her live stage debut as a solo artist - said: "After feeling unwell for the last few days I've sadly tested positive for COVID.
"I'm now self-isolating, following government guidelines.
"It means I'm no longer able to perform at Hits Radio Live in Birmingham this Saturday."
Jesy - who was due to perform at the event alongside the likes of Anne Marie, James Arthur and Tom Grennan - has also offered an apology to her fans.
The singer - who quit Little Mix in December 2020 - said: "Apologies to any of my fans who bought tickets and I'm so sorry I can no longer be there. I hope you all have an amazing night, stay safe and I can't wait to see you all soon - love you all so much."
Jesy is particularly frustrated about the timing of her illness, as the upcoming event represented a landmark moment in her solo career.
A source told The Sun newspaper: "Jesy is gutted.
"She was so excited to get back on stage but COVID has put a massive spanner in the works.
"Luckily her schedule had down time pencilled in but the show was going to be her big live comeback.
"She still plans to perform at next month's Jingle Bell Ball as previously announced."
Meanwhile, Jesy previously explained that she was quitting Little Mix because being part of the pop group had "taken a toll on [her] mental health".
The singer took to social media to reveal why she decided to leave the chart-topping girl group, which also includes Jade Thirlwall, Perrie Edwards, and Leigh-Anne Pinnock.
Jesy said: "I find the constant pressure of being in a girl group and living up to expectations very hard."
Tagged in Little Mix Jade Thirlwall Jesy Nelson