Medical guidance doesn’t describe a diabetic foot ulcer healing without treatment, and much of it describes what happens when one is left.
The first step is to follow your provider’s instructions on how to treat the ulcer.
Untreated ulcers can lead to serious harm. Untreated foot ulcers are the most common reason for toe, foot, and leg amputations in people with diabetes. Foot ulcers are also a common reason for hospital stays for people with diabetes.
There are reasons this wound in particular does not resolve on its own. Diabetes can damage the nerves and blood vessels in the feet, so injuries are more likely and may not heal well. Foot ulcers are partly caused by too much pressure on one part of the foot — pressure that continues unless something is done about it. Sometimes putting pressure on a healing ulcer for even a few minutes can reverse the healing that happened up to that point.
Some treatment is not something you can do yourself: debridement removes dead skin and tissue, and you should never try to do this yourself.
Waiting is also harder to judge than with other wounds, because the usual signal is missing. Diabetic ulcers are often painless, because of decreased feeling in the feet.
Slow is not the same as stalled, and healing does take time: it may take weeks or even several months for foot ulcers to heal. But that timeline is for an ulcer being treated, not one being waited out.