The actress might be unable to perform this weekend's dance after suffering a back injury.
Natalie fell over while practising the fast-paced quickstep with her partner Artem Chigvintsev. She underwent a cautionary MRI scan on Wednesday for a slipped disc and has been ordered by doctors to rest for at least 48 hours.
"The medical team certainly found some swelling on Natalie's back. She's planning to see a consultant and is putting her feet up for a few days," a source told the Mirror.
"Everyone is hoping she will still be able to dance, but it is all hanging in the balance at the moment."
Partner Artem has also expressed concern for the 29-year-old. "We had to finish rehearsals early on Tuesday because of the pain in Natalie's back – if it is serious she might not be able to continue in the competition," he revealed.
Natalie has already proved herself a talent on the dancefloor, topping the leaderboard last weekend with a score of 36 for her rumba.
Should she recover before Saturday, she will perform a quickstep to Yeah by Usher.
The former Coronation Street star hit headlines earlier this week when she received criticism from some viewers for her previous dance training.
It has emerged that she was listed as a 'highly skilled' dancer on her CV, and worked professionally until she suffered an injury aged 19.
Natalie, who started training when she was four, was previously credited for her abilities in cabaret, jazz dancing, contralto, Latin American and tap dancing.
Former Strictly star Denise Van Outen is among those who have come to Natalie's defence.
Denise faced similar criticism because of her theatrical training, but said that while many people believe training gives contestants an unfair advantage, it can actually prove a hindrance.
"People need to understand that the style of dancing you do on that show is so different," she said.
"A lot of people that go on Strictly have had some form of (theatre training), so I don't think that Natalie has got an unfair advantage.
"Sometimes it's a hindrance. If you have training in one other form of dancing, sometimes you have to break habits."