If it's a small enough piece, he'll pass it and be fine. Check his poop for it. It could get stuck, though, so watch out for not going at all, diarrhea, vomiting, loss of appetite, not laying down, pacing, panting and crying.
If he's doing any of that, you need to take him to a vet, particularly if you haven't seen the piece come back out and its been several days. Bowel obstructions can be deadly, so don't wait and see if he's showing symptoms.