The strongest man on the planet and the baddest dude on "Game Of Thrones" says there's no way in hell he could fight Deontay Wilder or Tyson Fury ... 'cause The Mountain says they'd END him!
We got Hafthor Julius Bjornsson -- aka Thor, the 2018 World's Strongest Man -- out at LAX when he told us if he fought the heavyweights ... it'd be lights out for him.
"Right now they are the best, and there's no way a guy like myself that doesn't train in the sport can just go in there and beat them.