The singer has revealed she is undergoing physiotherapy in the hope of it getting better in time for the weekend.
Sophie Ellis-Bextor and dance partner Brendan Cole
She told The Sun: "My knee really hurts. I had to have physio on it three times last week.
"I hope I can go one more week. I’m sure I will because I’m enjoying myself so much."
Meanwhile, the song list and dance styles the couples will be taking on have been revealed.
Susanna, Abbey, Sophie and Natalie will now battle it out in the final
Sophie Ellis-Bextor and Brendan Cole will perform the Viennese Waltz to 'My Favourite Things' by Julie Andrews (judges' choice); 'I Wanna Dance with Somebody' by Whitney Houston (showdance) and the Charleston to 'Rock It for Me' by Caravan Palace (couples' favourite).
Abbey Clancy and Aljaz Skorjanec will do the Waltz to 'Kissing You' by Des'ree (judges' choice); 'Sweet Child o' Mine' by Guns N' Roses (showdance) and the Quickstep to Katrina and the Waves' 'Walking on Sunshine' (couples' favourite).
Susanna Reid and Kevin Clifton will dance their Quickstep to Tommy Steele's 'Good Morning' (judges' choice); 'Your Song' by Ewan McGregor (showdance) and Paso Doble to Carmen's 'Los Toreadors' (couples' favourite).
And Natalie Gumede and Artem Chigvintsev will perform their Cha Cha to Boney M's 'Rasputin' (judges' choice); 'Steppin' Out With My Baby' by Christina Aguilera and Tony Bennett (showdance) and the American Smooth to Jennifer Hudson's 'And I'm Telling You, I'm Not Going' (couples' favourite).
The 'Strictly Come Dancing' final airs on Saturday at 6.30pm on BBC One.