My ducks circulation was cut off can you help?

My duck had a band rapped tightly on its leg that i had not noticed. Nearly a week went by and I noticed the string after seeing its foot had turned purple. (My duck is free range so I didn't notice the string soon after it was caught up) - brother told me he saw the string a week prior. I am worried because he has been limping and I was wondering if you could tell me weather the flesh will have a chance of reviving or if its necessary to put it down. I am not in a good finacial place right now so a vet would be 98% out of the question. Please Help! Anything that could help my duck feel better and revive. His foot had a small 'pouch' i guess you could say if that helps and also he got a cut on that foot and it DID bleed, is that a good sign? Thanks.