Safety collar failed

Sat outside today and seen my neighbours male cat limping past as many cats do he wonders for a day or two at a time sometimes a bit more.
Anyway thought bit odd he's limping so checked and the safety clip for the collar had failed he had obviously fallen from a tree long story short he is not in good shape he has a very deep cut which has been irritated by the flee repellant the vets have basically said that if antibiotics haven't started working or if he gets worse pain wise stops eating or drinking he will have to be put to sleep!!!!! Such a shame he's not even two if it wasn't for a dodgy safety clip he would be fine!!!