The former Coronation Street actress and her pro partner Jared Murillo will be allowed a week off from the competition while she recovers. Murillo and O'Brien were supposed to dance the rumba this week and the American dancer had brought over seven family members from his home in Utah to watch his performance.
Speaking to the official show website, O'Brien said: "I am devastated. I was so looking forward to this week's show. Jared and I have spent so much time and effort on a really fantastic routine and I just couldn't wait to perform it on Saturday.
"Hopefully I will bounce back quickly and be on top dancing form soon, ready to come back straight into the next routine. I will be watching them all this weekend."
Strictly rules state that competitors are allowed one week where they can be given a bye due to illness or injury. If O'Brien is still unable to compete next Saturday, she will be forced to leave the competition.
All the other 12 celebrities will dance as normal this weekend and one more person will be eliminated on Sunday's results show.