I have seen the pic which you have sent. The deep wound is most likely to be 3rd degree wound in some parts. So, if you wait for natural healing than it wont heal completely, even after prolonged period of conservative management. It may lead to deep scar tissues around ankle and foot, which will cause you cosmetic problem in future. So, if the wound is 3rd degree than skin grafting remains a good choice for better healing process. If you donot want skin grafting due to economic cause than it will be your personal decision. Consult your doctor also if you have further queries.