To me it looks ok. I am not a vet. Send a pic to your vet when they are in the office, or call. Doesn’t look to me like a problem unless your cat obsessed and won’t leave it alone.
How long ago was he neutered? I can't tell much from the pic, but you want to look for any swelling as well as seepage (pus or blood). It may be that he pulled a stitch (if there were any) and the incision is a bit open. Try to take a clearer pic and send it to the vet to ask their opinion.