Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Seek emergency care if the foot or toes suddenly become pale, blue, or cold, or if you develop severe pain with loss of feeling or movement.
These signs may indicate a problem with blood flow or a serious injury rather than Morton neuroma.
And for anyone, someone who:
Get prompt medical advice if you cannot put weight on the foot, especially after an injury.
A fracture or another injury may need to be ruled out.
Seek urgent assessment if this occurs, particularly if you also have a fever, a wound, or feel unwell.
And for anyone, someone who:
Arrange a routine appointment if forefoot pain lasts for more than a short period, keeps returning, or is interfering with walking, work, sleep, or exercise.
You should also seek assessment if numbness is persistent, spreading, or affecting more than two nearby toes.
The article also says
A red, hot, rapidly swelling foot is not typical of Morton neuroma.
If you have diabetes, reduced circulation, or reduced feeling in your feet, seek help earlier for new pain, swelling, blisters, or skin damage.
Every sign above is quoted from the sofidex article on Morton neuroma. If you are not sure, err upward — it is always reasonable to be checked.