I had farriers tell me the same thing, sadly on the horse it cracked open. Do not wait find a very good farrier that will put the proper shoes on and if needed during the day boots.
I use unflavored gelatin in his pellet feed and it works wonders. Heal it from the inside out. It will grow out but it will depend on how fast your horses hooves grow.
I also use hoof hardener that help also. I have tried other stuff on the market and it just does not work as good nor as fast.
I hope this helps some.