Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services if foot drop appears suddenly with possible stroke signs, including facial drooping, arm weakness, difficulty speaking, sudden vision loss, severe loss of balance, or an unusual severe headache.
Emergency assessment is also needed for foot drop with signs of serious pressure on the nerves at the bottom of the spine.
These include new loss of bladder or bowel control, numbness around the genitals or buttocks, or rapidly worsening weakness in both legs.
Seek urgent assessment after a major back, hip, knee, or leg injury, particularly if the foot is weak, numb, cold, pale, or very painful.
Arrange a prompt medical assessment for new, unexplained foot drop, even if it is painless.
Seek prompt review if weakness is spreading, worsening, or accompanied by significant back or leg pain.
When the cause is known and symptoms are stable, attend routine follow-up.
Report repeated falls, reduced walking ability, joint tightening, or brace problems.
Persistent redness, broken skin, or a sore beneath a brace should be assessed rather than left until the next routine visit.
Every sign above is quoted from the sofidex article on Foot drop. If you are not sure, err upward — it is always reasonable to be checked.