Male cats, especially neutered ones are prone to stones blocking the ureter and they may bleed from their penis. Other signs are loud distressful meowing when trying to use the litter box and going in and out frequently but no urine is seen.
If this happens take him to the Vet immediately. If it is a stone that’s blocking the ureter and blocking urine from leaving the bladder it can be fatal as the bladder could rupture with too much urine in it.
My male cat will be 8 years old in May and when he meows loudly around the litter box and goes in, I listen and then check the litter box when he’s done to make sure he was successful in his endeavers.