Cats do get diarrhea. Have you changed his diet? Changed to a new dry food or added canned? That can upset a kitty's stomach. Do you have any plants in the house that he may have nibbled on??

It could be a number of things. You can try adding cooked rice or pumpkin which will help "firm up" his poos.

Pinch him gently by the nap of his neck. If his skin stays up, that means he's dehydrated. Might want to take him to the vet for a looksy.

Unless you notice a change in his eating habits, litterbox habits (blood in his poos or going outside the box), or his overall personality (i.e., lethargy, vomiting, weakness, etc.) I'd just keep an eye on him. If you're really concerned, I'd definitely at least put a call into the vet. He may be able to suggest something or tell you to bring him in.

Good luck and please let us know how you make out.