Boss took a hit to the head when he was on the ground after a 29-yard catch at Buffalo Week 2 (see picture below). The Star reported that doctors told Boss they would not clear him to play this season.
In his first five years in the league, Boss only missed seven games. The Chiefs signed Boss in the offseason to give them a blocking tight end to play alongside Tony Moeaki. They had plans to use both at the same time, similar to how the Patriots play both Aaron Hernandez and Rob Gronkowski.
It's unlikely that the Chiefs will add a tight end to replace Boss. They have used Steve Maneri in Boss' place the last two weeks. They converted Maneri from offensive tackle to tight end during the offseason. They also have Jake O'Connell.