Take him to the vet definitely,it could be one of many things.

Unfortunately if you have a tom with the full set of tackle they will disappear and go into the most dubious places and any female they can get hold of.
If you want him to stay near home and out of trouble ask the vet to do a little "snip"

My lads are all done and the ones that are allowed never wander far.

Hopefully he'll be ok and nothing serious