Danger of a collar on a community cat

Someone, likely his ex-owner, put a collar on him and dumped him in an industrial car park. The collar has slipped to his shoulder. It must be very uncomfortable to walk. He is fortunate not to have the collar entangle on some hook-like object resulting in strangulation.
This morning, he was trapped for sterilisation. He will be released 2 days later, with the collar taken off.