Are bunnies nails long? Its quite possible he had snapped a nail above the quick. Do you have any cornflour in? Check if you can that the bleeding is coming from the nail. If it is, try dipping the buns toes into a bit of cornflour, it can help staunch the bleeding. Styptic is even better, but you must ensure none of it gets on the animals skin. Keep your rabbit calm and quiet, this is important because if he stresses, his heart rate will increase and he will most likely bleed even more.
Dip toes, blow off excess (away from face) dip again, blow, dip again and blow. This should help ease the bleed. If it dosent, it's a trip to the vet. If it's a cut or a wound in the pad, this, in my oppinion, needs a vet to check it over anyway. It may need a little stitch and some antibiotic ointment, as bunnies arnt overly fussy if they stand in dirt or their own poo etc, so you have to be aware of the chance of infection.
Hope little chap is ok!