Jason Witten has a spleen injury, a sourced told ESPN's Ed Werder. The injury was suffered on the Monday Night Football game against the Oakland Raiders. 

There is a chance that Witten could miss the first game of the season, which would come against their arch nemesis New York Giants on September 5th. 

The spleen was not ruptured, but there was internal bleeding. Despite the seriousness of the injury, the tight end could avoid surgery. 

In case fans do know where the spleen is located, we have an image for you.

The injury came early in the second quarter. Announcers Jon Gruden and Mike Tirico noticed how hard Witten was hit on an 8-yard pass from Tony Romo.

Witten was popped from behind by the Raiders' linebacker Rolando McClain. Witten was removed from the game immediately following the hit. 

The tight end is the most important player for Romo on the offense. Witten has been Romo's biggest weapon. He knows the playbook and he is as consistent as players come. 

Last season Witten led the Cowboys in reception with 79 and yardage with 942. He finished the season with 5 touchdowns. 

Needless to say, without Witten, the Cowboys cannot succeed and make it far into the season.

The good news is that he will miss the remainder of the preseason with a chance of returning for the opener.