Wood pigeon found on ground in U.K.

Rescued a wood pigeon this morning from the side of a busy road. It was moving itself with the use of it wings along the ground. On inspection it looks as though the fantail is all stuck together - matted up. It wasnt using its feet either just its wings to pull itself along. I havent wanted to inspect it any further as I would like it to have some peace and quiet in the box I've put it in.
A neighbour then told me she had heard a flapping noise at the back of her shed on Friday 19th June (Mon 22nd today) but thought nothing more of it. She went away and came back Sunday and could still hear the noise. When she investigated she found the little soul in a bucket on its side at the back of her shed. She released it, attempted to feed it and hoped for the best. I then found it a short distance away this morning.
Has anyone any ideas what could be wrong? When I phoned the vet they just said bring it in and we can put it to sleep. This is fair enough if the bird is suffering and I would not wish to prolong this in any way. But it just seems so fiesty. I would love to give it a fighting chance. Any suggestions would be gratefully received. Thank you