TOKYO, Oct 21 (Reuters) - Wales backrower Josh Navidi has been ruled out of the remainder of the Rugby World Cup after tearing his hamstring during the first half of Sunday's quarter-final victory over France, coach Warren Gatland said on Monday. Gatland told a news conference that he would be replaced with a back, rather than another forward, due to concerns over others in the squad, principally centre Jonathan Davies, who missed Sunday's match. (Editing by Alex Richardson)