It doesn't look too bad to me. if it were me , I would just keep watching it to make sure it heals up good. He's not licking at it, is he ? if you saw some yellowish discharge , I would think infection... but, to me it does look alittle red, alittle bit raw, and alittle crusty like you said , but, I think it will heal up fine. I would watch it for and see how it looks. if it gets worse, then def. call to have them look at it.