No, you can't. you need defeat all 3 warzones bosses first to have the chance to fight against Ancient Spawn of Morgathla. also you need 3 itens items to fight him.
Mallet HeadMallet Head, dropped by The Baron from Below from Warzone 4;
Mallet HandleMallet Handle, dropped by The Count of the Core during Warzone 5;
Mallet PommelMallet Pommel, dropped by The Duke of the Depths during Warzone 6.