Brent Cockbain has warned Grand Slam-chasing Wales of the "hero to zero" danger facing them in next Sunday's RBS 6 Nations Championship clash against Scotland.
Wales will travel to Edinburgh following successive victories over England, Italy and France, results which have left them just two more wins away from achieving a first championship clean sweep since 1978.
Unbeaten rivals Ireland arrive in Cardiff on Saturday week for a potential Grand Slam showdown but Wales head to Murrayfield knowing they have triumphed just once in 20 years at Scottish rugby headquarters - a 34-19 verdict eight years ago.
"As long as we are not complacent and we play our game, then there is no reason to be fearful of them," said Neath-Swansea Ospreys lock Cockbain.
"The trouble is, everyone expects us to get a win up there, and it's not the case in international rugby that you just turn up and favourites win.
"Look at last weekend in Paris. France had every right to win that game, and probably should have won the game, then we turned them over.
"So a bounce of the ball and a referee's decision, and we could be out of a Grand Slam, Triple Crown, everything. We really have to go up there with all guns blazing, and play our game.
"Everyone's focus seems to be on the other game (Ireland), which I won't even mention, but this weekend is the game for us. If we lose this weekend, then we go from hero to zero overnight," he added.
"We have to work hard and keep pushing ourselves. We can't relax at all. It will be the biggest test so far, I think, of us."
England's preparations for the Autumn International series were potentially dealt a further blow as Maro Itoje was forced to undergo an x-ray after Saracens' European victory over Scarlets on Saturday night.