Kitty Konundrum

We have an office cat. Or rather one that decided to wander into our
office and make himself right at home. he is the most friendly ginger
tom you've ever seen but really doubt that he's feral considering how
clean he is each morning.
There is one rather major concern though. He has a lumpy head. Not an
issue most people would say but he has this really massive one that's
developed scar tissue now. So here's the issue:

Take him to a vet or hope that his owners will?

I would attach some kind of message to his collar were it not for the
fact that he doesn't have one.