Not quickly I am afraid although yes. It could be stripped down and put together. With the right preparation you could have the gun ready when u need it and use a pistol for self defence. Alternatively i think there is a version with a folding stock/he could add a folding stock which would knock about thirty centimetres off. It could be hidden in the rucksack then. Just about. 

I'm going to have to sleep now I am afraid.