The 17-year-old has been put on bed rest by doctors after she cancelled a performance in Liverpool on Wednesday night.
The singing hopeful shared her disappointment on Twitter, writing: "So sorry that I’m missing tonight in liverpool! Need to be on strict voice rest ahead of the biggest week of my life, it needs to be perfect."
A spokesperson for X Factor told Metro.co.uk: "Unfortunately Louisa is unwell and we have been advised by doctors that she currently needs to be on bed and voice rest ahead of this weekend’s final.
“We’re sorry to disappoint anyone who was looking forward to supporting her at her performance in Liverpool today."
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If Louisa is too ill to perform at the final, it will be down to Che Chesterman and Reggie 'N' Bollie to battle it out for this year’s title.
It’s not the first time Louisa has been hit by health problems.
At the Judges' Houses stage of the competition in LA she complained of severe headaches, which was later revealed to be a result of a wheat intolerance.
Che Chesterman and Reggie N Bollie could be fighting it out in the final without Louisa
She said at the time: ''Unfortunately I had a bit of a tough time. I woke up on the morning of my performance with an awful headache that got worse as the day went on. They called a doctor who diagnosed me with a wheat intolerance, which can cause headaches."
A show source told The Sun: “Louisa is putting on a brave face but she can hardly speak. We’re worried she could be too ill to continue next week. We couldn’t give her a free pass to the final, there would be uproar.
“But if any of the other contestants come down with the same thing we will really struggle. Olly is also sick and struggling. The bugs going round at the moment are really nasty.”
Earlier this week, it was confirmed that Leona Lewis will be making a return to the ‘X Factor’ stage to perform at the final, despite a high-profile departure from Simon Cowell’s record label last year.
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