oh geez...if it is bleeding still apply light pressure to it with a tissue or something momentarily then see if you can dip it in flour to stop the bleeding if it won't after applying a bit of pressure. It probably hurts him a lot so careful
I've not had this happen before so just taking a guess at what I would do. Hopefully someone will come along to advise further.
Likely you will need to remove the wheel so the toe can heal and keep it very clean with foot baths for a while.