TEMPE, Ariz. -- The Arizona Cardinals need an insurance policy for their insurance policy.

With the news Monday that running back Chris Johnson suffered a fractured tibia in Sunday's win over San Francisco, the Cardinals have lost the engine of their running game. This might be the most damaging injury the Cardinals could have suffered aside from quarterback Carson Palmer.

This might have just cost the Cardinals the Super Bowl.

Aside from injuries, one of the major differences from last season was the addition of Johnson. He instantly made the Cardinals' offense dangerous, especially when coupled with Palmer's arm and a deep wide receiving corps.

Johnson made the offense tick. He made defenses play the Cardinals honestly.

Until he walked off the field in the third quarter Sunday at Levi's Stadium, Johnson added a dimension to the running game that Andre Ellington couldn't last year, regardless of whether he was healthy or not.

With Johnson in the backfield, Arizona's offense flourished, becoming the highest-scoring unit in the NFL. They were versatile and dynamic. Defenses couldn't ignore the run game. Arizona was averaging 4.1 yards per carry as a team this season -- up from its league-worst 3.29 average in 2014.

Johnson alone was averaging 4.15 yards per carry and was flirting with the league lead in rushing a few weeks back. He finished Sunday fourth on the current rushing list.

Johnson declined several teams this offseason because he wanted to play for a team that could play into January, and he's rewarded the Cardinals for taking a chance on him when other teams stayed away. He was on pace for 1,184 rushing yards, which would have returned him to the 1,000-yard club after a one-year hiatus and would have made him the first Cardinals running back since Beanie Wells in 2011 to rush for 1,000 yards or more.

But the true impact of Johnson's injury might not be felt until later this week, when the Cardinals determine if Ellington will be able to play Sunday in St. Louis with a turf toe injury.

Without Johnson or Ellington, the Cardinals' offense could be in all sorts of trouble. With a source telling ESPN NFL Insider Adam Schefter that the Cardinals are still determining if Johnson can return before the season ends, the running game will be in Ellington’s hands in the meantime -- if he can play.

However, for as dynamic and talented as Ellington is, he's struggled to become the effective every-down back that Johnson was. And his turf toe injury won't be helping Ellington's reputation for being injury prone. So for the time being, at least, the onus of the run game will be shouldered by a rookie, David Johnson. While he's shown flashes of talent and brawn, Johnson has lately reminded Arians he's just a rookie by struggling to pick up hots and blitzes.

As the layers of Chris Johnson's impact are peeled back, the more the Cardinals will miss him. And maybe miss a chance at a special season.