When I read your post I thought at first it might be a tick but that's not what it looks like on the photo.
It could be a wart, cockers seem to be prone to them. Morgan had to have one removed from his forehead because he kept bashing and scratching it which made it bleed.
The other possibility that came to mind was that maybe he'd had a tick which then fell off as they can often leave little lumps behind afterwards.
