A Buckingham Palace source said the sprain was unrelated to the unspecified ailment that caused the queen's hospital visit, calling it an "incredibly unfortunate coincidence."
But Elizabeth's absence from an engagement she sees as one of the most significant of the year will increase concerns about her health.
The ceremony would have been the queen's first in-person public engagement since she was advised to rest after spending a night in hospital on Oct. 20-21.
In her 69 years on the throne, the monarch had previously missed the event at the Cenotaph War Memorial in central London only six times, four while on tour abroad and twice while pregnant.
Thousands of veterans later marched past the Cenotaph, led by the band of the Coldstream Guards.