The singer was suffering breathing difficulties but still managed to wow fans with her performance during the Aussie leg of her Back to Basics tour.
However, things got bad when Aguilera, who is reportedly expecting her first child with hubby Jordan Bratman, collapsed backstage.
Doctors who rushed to treat her forced to her to skip songs and ditch her encore, fearing that it would be too much for her and the baby, reports The Sun.
They then kept the 'Dirrty' singer under observation, and also ordered her to cancel her remaining two Melbourne dates in lieu for total bed rest.
But Aguilera's team is keeping mum about the pregnancy, with the official line insisting that she was suffering from flu.
"I want to personally apologize to all of my fans for having to cancel my last two shows here in Melbourne. Unfortunately, I have fallen ill with a bad flu virus. This is one of the best cities in the world to perform in and I am truly disappointed that I won't be able to share my show with you all. Thank you for all of the continued love and support and I hope to perform for you all again next time," the singer said in a statement.
A insider revealed that everyone was hoping that Aguilera would cancel her last two dates and get some rest, no matter how much she hates letting her fans down.
"The wardrobe department have been letting out her costumes to accommodate her growing tummy," the insider said.
"We have been told to keep it hush hush. She is a perfectionist and hates letting people down. But we're hoping she will cancel the last two dates and return to LA to put her feet up," the source added.
A source had previously told Star magazine that hubby Jordan Bratman was getting concerned about the effect her touring might have on her and the baby.
"Christina told Jordan that the doctor says it's totally possible for her to keep working and have a healthy, happy baby. But that doesn't mean Jordan is happy about it. Christina is the center of Jordan's world. He's naturally worried and overprotective. He's trying not to get angry with her, but he's probably frustrated that she can't see his point of view and at least cut back on her commitments a bit," the source said.