That's a tight spot.

While I agree the animal sounds like it is nearing the end, I would wait for owner consent. I would not do something that could open you up to a lawsuit. Now days people are crazy and if they see a way to make a quick buck they will.

If you do have to get a vet to put it down I would ask the vet for a detailed letter explaining the condition and the reasoning for putting it down.

Sounds like this guy should be confronted by your club.