It would depend on what kind of injury the bunny had. If it has a hurt leg then you can just try and make sure it has food till it gets well again or you could try and find its mother and send it on its way
Only qualified professionals should handle injured animals, especially if they are wild. If you suspect a wild animal is injured, contact your local Fish & Wildlife office so that they can take the proper course of action.
Deep lacerations and broken bones must be treated by a veterinarian. Less serious abrasions may be flushed and treated with iodine (spray-on products are available).