swellings around that sort of area can be to do with tooth infections, abscesses from eg. thorns getting in, potentially blood blister type of thing from having a knock, or even sometimes problems of deformity or infection of the bone itself.
If he is eating, drinking and doesn't have a temperature, see what it does over a couple of days.
If it is an abscess, it may well burst out, antibiotics in ruminants have a nasty habit of walling abscesses off so they don't burst or get any antibiotic into where it counts!
If it's a blood blister type, I would expect it to get softer and gradually disappear.
If it is a tooth problem, either a damaged or infected tooth, the problem will continue to build up.
If it's a problem with the bone itself, it probably won't change much.
Over the next couple of days, if it doesn't change and doesn't affect his appetite, then it may be nothing to worry about. If it changes as described, an abscess may need lancing or draining, and antibiotics once it's empty, a tooth problem may need further veterinary treatment, or whatever it is may resolve itself.
Hopefully it'll just settle down of its own accord, cos that's always easiest!
Suzanne