There was a jubilant atmosphere in Arrowhead Stadium on Thursday night after the Chiefs fended off the Raiders to take over first place in the AFC West. However, down in the locker room, a more somber mood proliferated.

Their heart and soul was just lost for the season.

During his postgame press conference, Chiefs head coach Andy Reid revealed that Derrick Johnson ruptured his Achilles. The injury will keep him out for the rest of the season.

At 10-3, Kansas City is in great shape to reach the playoffs, and they're currently positioned to earn a bye. But, they'll need everybody to step up to fill the void that Johnson's absence will create in the middle of their defense.

The injury occurred on a non-contact play. While shifting his weight from side to side, Johnson suddenly tumbled to the turf, grabbing for his left leg. He threw his helmet in frustration, fearing the worst.

Johnson has been the rock for Kansas City's defense for 12 years, ever since they drafted him in the first round in 2005. The four-time Pro Bowler played nearly every game until 2014, when he tore his right Achilles. He returned for all of 2015, and he played in all 13 games for the Chiefs this season.