Definitely start treating now. You can put him in a dog crate or something to let him start to heal up but I would definitely keep him I side for a while.
Ok, bad smell usually means infection. You need to being him inside. Flush the wound out very well with a saline solution, neosporin that hole up, and probably start him on an oral antibiotic. The only dosage I know is for tylan 200, not sure if that will help with this infection or not but the...
Are you treating it in any way? Do you k ow how it happened? I would definitely rinse it out with a saline solution then apply some plain neosporin (without pain relief) is there a smell?