At just six inches tall and weighing just over a pound, he is now in an incubator in the intensive care unit atTiggywinkles Wildlife Hospital in Buckinghamshire.
He has only recently opened his eyes.
Les Stocker, founder of Tiggywinkles, said: Rupert's mother had very severe injuries.
We brought him out and got him breathing and then he went into an incubator on oxygen. He is now being fed by a tube.