I do think that it is worth trying. It is true that sometimes mothers in the wild will push out offspring that has something wrong with it. However this is not always the case and I certainly know many "exceptions to the rule." If the rabbit came in contact with something that gave an unusual smell that the mother can pick up - it could be something as simple as that.
There should be rabbit formula available at a pet store. Keeping him warm, regularly fed and separated are good ideas. Due to the stress of being separated at this age, along with the potential of an underlying problem - the prognosis would be guarded. But if I ever have a guarded prognosis, I hope someone gives me a chance too. JMHO
