Please post pictures of your tortoise, including his shell, so that folks can provide assistance.
If you can also share information about your tortoise's age, weight, diet, lighting, and enclosure, that will help narrow things down. Leg problems can be a symptom of metabolic bone disease, which can be fatal. Lighting, diet, and enclosure information (on addition to photos) are needed to help identify this.
Take a real close look at the leg under a bright light, from the toes all the up inside the body, to make sure there isn't a hair or something wrapped around it.