Williams, 30, is currently taking part in the UK TV show but was rushed to a doctor when she was in pain following the fall.
The former Destiny's Child singer had an X-ray taken but there was no sign of a break so she was given crutches to walk on.
According to UK newspaper The Sun, a spokesperson for the show said: 'Michelle's ankle is very swollen. She is having physio treatment but has been advised she must have complete rest.'
It is not yet known if she will be able to take part in the next show on October 30.