But that is just what has happened. The Vikings went 10-6 and made the playoffs in 2012, but last week they couldn't beat the Cleveland Browns at home.
The Steelers missed the playoffs last season, after a spate of injuries in key positions. But the six-time Super Bowl winners are always tough.
Except they looked anything but tough getting annihilated on their own field by the Chicago Bears last Sunday. So just what is ailing the Vikings and Steelers?
On the surface it is easy to declare that one side of the ball is undermining each team. For the Steelers it is their offense. Or more specifically, the distinct lack of offense.
The main issue is in the running game. Despite seemingly possessing a cast of thousands at the position, the Steelers cannot buy yards on the ground.
They have certainly tried. Their efforts even involved signing former Dallas Cowboys flop Felix Jones and bringing back fumble-happy Jonathan Dwyer.
But still there is not even a hint of a running game. That has left quarterback Ben Roethlisberger at the mercy of heavy pressure.
Pass-rushing defensive linemen and free blitzers have routinely waltzed through Pittsburgh's excuse for an offensive line. Of course, this a front five not helped by the season-ending injury to stellar center Maurkice Pouncey.
It is a shame Roethlisberger does not have more time, because the Steelers still possess competent receivers. The underrated Antonio Brown joins Emmanuel Sanders and Jerricho Cotchery to form a useful group of wideouts.
The return from injury of tight end Heath Miller is also a boost ahead of the trip to London. What Pittsburgh do miss is the vertical speed offered by their former deep threat Mike Wallace.
He is now plying his trade for the Miami Dolphins. But when Wallace was a Steeler, opposing defenses had to keep both safeties deep. That meant less eight-man fronts to pressure Roethlisberger and stuff the run.
While the Steelers have found it hard to score points, the Vikings can't stop leaking them. They have allowed over 30 points in every game so far this season.
Despite a pass rush featuring ends Jared Allen, Brian Robison and Everson Griffen, the Vikings rank 28th against the pass. If the Steelers give Roethlisberger time, he will torment a woeful secondary.
Of course, it's no secret the Vikings will look to protect their defense by keeping the Steelers off the field. They will do it the way they always do, with star rusher Adrian Peterson running the ball.
It has been something of a feast or famine season so far for Peterson. He either breaks a long gain or incurs a loss. But the player who surpassed 2,000 yards last season remains Minnesota's chief threat.
Not too long ago, the Steelers would probably be the only team in the NFL who wouldn't sweat facing Peterson. After all, their feared defense has often been a nightmare for running backs.
But even their notoriously stingy rush defense is starting to decline. The Steelers currently rank 23rd against the run.
Ever since they ditched mammoth veteran nose tackle Casey Hampton, in favour of the lighter Steve McLendon, Pittsburgh's front has been far from formidable.
So maybe Wembley fans will get to see Peterson run wild after all.
Frankly, the Vikings need him to, because their passing offense is an accident waiting to happen and one that often does. That might change however, with rumours that injured, mistake-prone starter Christian Ponder could be replaced by Matt Cassel.
The Vikings and Steelers both come to Wembley with major issues on one side of the ball. But a deeper look also reveals reasons for concern on the other side.
With two teams blighted by this many problems and both desperate to win, a mistake-filled, but eventful encounter seems inevitable.
image: © Mike Morbeck