My duck is limping what can i do to help him?

dont say vet cause i know what the problem is. 2 days ago my dad was holding him (he is a mallard) and he accidently dropped him and his back claw fell of (like the claw on the extra toe that is behind his foot) and now he cnt walk so well. how long does it take to grow back? and what can i do to make it easier for him to walk?